desktop injection moulding machine

MT/HNDMECH/04/41 Page - 1 -

1. Introduction to Plastic Forming Process

Figure 1.1 Spectrum of Forming Process for Thermoplastic Materials

The above spectrum reveals about thermoplastic forming process. Even all these techniques are

available today, due to the time limitation and such factors, only little headings will be introduce on

this article.

Blow molding: a process of forming hollow articles by blowing hot polymer against internal

surfaces of a split mold. Usually, a tube of heated polymer is extruded down the center of the closed

mold. Air is then injected, and the heated polymer expands in a fairly uniform thickness to form the

desired shape. This is the process used to make plastic bottles and containers. It is fast and typically

used only on thermoplastic materials.

blow molding

calendering

sheet materials

injection molding

rotational molding

solid phase

forming

thermo forming free form

fabrication

film blowing

casting

extrusion


Calendaring: the process of forming thermoplastic or thermosetting sheet or film by passing the

material through series of heated rolls. The gap between the last pair of heated rolls determines the

sheet thickness. The material usually is blended and plasticated on separate equipment. Elastomer

sheets, gaskets, and vinyl flooring tiles often are formed with this process.

Injection molding: A process in which granular polymer-usually, thermoplastic- is fed from a

hopper into a heated barrel where it is melted, after which a screw or ram forces the material into a

mold. Pressure is maintained until the part has solidified. The mold is opened, and the part is ejected

by some mechanism. This is by far the most important techniques for mass production. The major

disadvantages of the process are that not all polymers can be processed (some thermosets cannot)

and the metal molds are very expensive.

This basic process is also used for coinjection molding of two different polymers. There are two

extrusion barrels and injection systems. A shot is made with one polymer, and a second shot with a

second polymer can be used to surround or surface the part made in the first shot. Co-injection is

often done to achieve a cosmetic effect or to alter properties use properties. For an example, a

thermoplastic elastomer (TPE) can be injection molded just on the grip area of a plastic drill body

after the rigid plastic body is molded.

Another variation of injection molding is structural foam molding. The mold is only partially filled,

and the injected plastic expands to fill the mold to produce a part that is lightweight because of the

entrapped porosity, but with an integral skin. Foamed polymers have lower weight (and cost) than

their non-foamed counterparts, and the mechanical properties are often comparable. This process

frequently is used on polyphenylene oxide, olefins, vinyls, nylons, and thermoplastic elastomers.

Figure 1.2: Blow molding (recycledplastic 2014)


Rotational molding: this process is usually used for manufacture larger hollow containers such as

fuel tanks, water tanks, floats...etc. a pre measured quantity of thermoplastic pellet is charged into a

closed metal mold. The mold is clamped closed and put into a device capable of rotating the mold

about two axes. The rotating mold is heated to melt the charge. The molten polymer forms a skin

against the mold wall to make the part. Mold heating is stopped, and the mold is air or water cooled

to allow part removal. A significant advantages of this process is that it uses relatively low-cost

tooling, compared with injection molding and other capital intensive process.

Solid-phase forming: a process employed with thermoplastic materials in which a sheet or similar

pre-form is heated to the softening process, but below the melting point, and forged into a drawing

ring by a heated die set; the still-worm perform is transferred in the draw ring into a cooled draw

die, and plug draws the part to the finished shape. A lubricant is applied to both sides of the perform

to assist the draw. Depth-of-draw ratios can be 1:5 or higher, and the forming in the solid phase is

said to enhance strength over parts formed by melting technique.

Simpler shapes can be made by heating and stamping a sheet to make a form such as an arch

support for a shoe. Filled or reinforced thermoplastics, called sheet or bulk molding compounds,

can also be formed by press shaping of the preheated material.

Extrusion: the process of forming continuous shapes by forcing a molten polymer through a metal

die. Extrusion is used to make structural forms such as channels, bars, rounds, angles, tracks, hose,

and countless other forms. It is very fast and usually applied only to thermoplastics. With special

techniques, two different polymers or different colours of the same polymer can be coextruded, and

plastic also can be foamed during the extrusion process. This process is often used to make

specially shaped weather stripping. A variation (blowing) is used to make plastic bags.

Figure 1.4: polymer extrusion (avplastic 2014)


As above processing techniques review thermoplastic forming process thermosetting plastic also

important under this heading. Because, thermosetting is important same as thermoplastic. For more

knowledge access British plastic federation-2015

Compression molding: the molding material, usually preheated and premeasured, is placed in an

open mold cavity, the mold is closed with a cover half or plug, and heat and pressure are applied

and maintained until the material has filled the cavity and curves. This is the most widely used

process for thermosetting materials. Because, curing of thermosetting polymer is a time-dependent

reaction, cycle times usually are much longer than those in injection molding.

Foam processing: various techniques are used to produce molded plastic parts with dense skins and

high porosity in the core. The simplest process involves charging a metal mold with resins that

foam and expand during reaction. The expansion of the foaming resin causes the mold to be filled.

A variety of similar process are used for large parts, with the exception that the polymer is injected

into the cavity rather than charged into the mold. Standard injection molding machine can be

adapted to produce foamed parts by adding equipment to inject a metered amount of gas or a

chemical blowing agent into the polymer near to exit end of the extruder barrel of the injection

molding machine.

Reaction injection molding machine: in this process the polymer reactance are pumped under

high pressure into a mixing chamber and then flow into a mold at atmospheric pressure. The

chemical expand to fill the mold and to foam the polymer. The foaming action of the reactant

produces the pressure for the application of mold details (~207kPa) , and the reaction heat speeds

the polymer cure. A schematic of the reaction injection molding is shown in FIGURE () this

thermoset forming process

compression molding

foam processing

reaction injection molding

injection molding

Transfer molding

Casting Sintering Vulcanization


process is most often applied to large parts (over 1kg), and polyurethane foams are the most popular

molding material. Many large auto parts such as bezel, dashboards, and fenders are made with this

process. Fillers can be added to the reactants to improve the mechanical properties of the molded

parts.

Casting: this manufacturing process forms solid or hollow shapes from molten polymer or from

catalyzed resins by pouring the liquid material into a mold, without significant pressure, followed

by solidification or curing. The mold is usually open at the top. The polymer casting process is

widely used on polyurethane and silicone elastomers to make roll covers die springs, sheets and like

that. It is also suitable for making jigs and fixtures from filled epoxy or resins.

Sintering: used on some of the fluorocarbons and polyamides, and similar high temperature plastics,

sintering is the bonding of adjacent surfaces of powder particles. Some of the high-temperature

polymers are made into shapes by compressing polymer particles, as in compression molding, and

heating them until the particles join by coalescence. They do not melt and flow as in normal

compression and transfer molding

Able see some polymer processing methods on above paragraphs. More knowledge can be gained

on plasticindustry.com (2015) under the heading polymer processing methods. This research

reduced the heading of this project. Because its not the plot of this project Let’s move onto the next

chapter

2. History and Revolution of Injection Molding Machines.

The website avplastic.co.uk says as plastic or plastic revolution starts 1847 by Jons Jacob Berzelius

as producing first condensation polymer to the world. Later 1861 another Britain scientist

Alexander Parkes invented first man-made commercial plastic. Even the Parkes invented 1861 the

plastic, he describes the creation 1862 International exhibition in London. He called this plastic with

Figure 1.5: reaction injection molding process (avplastic 2014)


the name “Parksine”. It was expensive to produce, flammable, and brittle. But it was able to heated,

molded and retain its shape once cooled.

American inventor John Wesley Hyatt 1868 developed celluloid by combining cellulose nitrate and

camphor as a substitute for ivory in billiard balls. He improves on Parkes’ invention so that it could

be processed into finished form. Around 1872 John Wesley Hyatt, take his brother’s help to

produce first injection molding machine as shown in figure 2.1. It was like a hypordermic needle. In

that machine, working substance melted through heaters and press onto a die by a plunger to take

desired part.

With a small break, around 1909 Belgium inventor Leo Hendrik Baekeland introduced

phenolformaldehyde plastic. He called it as Bakelite, because of, it is his own creation. 1930s Saw

the initial development of major vinyl thermoplastics still used widely today: polystyrene, PVC

(polyvinyl chloride) and the polyolefins. During this period, the ICI laboratories produce Perspex

(polymethyl methacrylate).

In 1938, now days widely using polystyrene invented by Dow and a very good demand created by

the World War II on following Dow inventions. During the 1945-1955 periods, several materials

Polyethylene, polystyrene including metals, leather, woods…etc. also produced cheaply. The help

of American inventor James Watson Hendry on this time duration, should not be forget at this

moment. He replaced a screw to plunger and created fully deviated John Wesley Hyatt machine.

Therefore, customers were able to access colourful plastic. Further, the frictional force producing by

Figure 2.1: Patent application of Hyatt's injection moulding

machine. (avplastic 2014)

http://en.wikipedia.org/wiki/Leo_Baekeland


the screw creates some amount of heat. Therefore, the requirement of heater band on machine

reduces and increase efficiency of the machine.

At 1955 to 1965 one decade time period, several more useful plastic introduced, HDPE, LDPE,

ABS are such plastics to remember at this moment. The creation of reciprocating screw is so

important to remember on this 1 decade period. It was able to moves backwards and forwards

during the mold cycle. After mixing, the screw stops turning and the entire screw pushes forward,

acting like a plunger for injecting material into a mold. During plastication, the screw moves

backward against the hydraulic back pressure.

At the year of 1970, a big revolution had created by James Watson Hendry by adding gas-assisted

injection molding process. The process helped to cooled down the hollow and complex work-pieces

quickly. It changed flexibility as well as the strength and finish of manufactured parts while

reducing production time, cost, weight and waste.

Due to the heavy demand for plastic, robots introduced at the year of 1972 and plastic overtakes

steel industry at the year of 1979. At the year of 1985, Japanese firm produced all electric molding

machines. At last on 1990, aluminum molds introduced for this industries. Therefore low cost

molds were able to produce.

(A)

(B)

Figure 2.2: A-patent drawing for the Hendry injection molding machine B- Drawings for the Willert

reciprocating injection molding machine (avplastic 2014)


3. Modern Day Injection Molding Machine

Previous chapter described the history of injection molding machine. Even there are several

revolutions occurred for injection molding machine from 1847, the machine can be broadly

classified as clamping unit, and injection unit. These two units are similar to trailer and engine set

of a container. There are no limitations to set trailer and engine. Any engine part satisfies to any

trailer set. Likewise, same case occurs at these machines. But small limitation such as shot size and

injection unit capacity determines their combination. The aim of those clamping and injection unit

can be view below

3.1. Injection Unit:

The injection unit performs several duties to the machine. It contains several components as heating

cylinder, hopper, injection screw, nozzle…etc. due to, these components are important: small

description are given on coming paragraphs.

3.1.1. Heating cylinder

Heating cylinders or the barrel is the heart of the machine. Here the only area the solidified plastics

turn to liquid or semi-solidified phase. There are several failures occurred for injection screw by the

improperly working heating cylinders. Normally the barrels are constructed by the two different

materials. Inside wall of the material is by a small layer of chromium content material for with stand

high abrasive nature of the injection process. Meanwhile, the external wall or entire barrel made

with inexpensive material.

Electrical heater bands are strapped for external wall of the barrel as covering the entire barrel as

shown in figure 3.1. The heaters are divided for three zones as rear, center and front. The each three

zone are control separately by separate temperature controllers. There are sensors and thermo

couples as the machine requirements to sense the zone temperature as one thermocouple covering

one zone.

3.1.2. Hopper

This is the place machine store its working material for around two hour time period. Normally the

hopper is vertically mounted to insert plastic by the gravity to the machine in the shape of cylinder.

The size of the hopper determines by the normal cycles and average part size the machine can be

produced.

The pallets which introduced to the barrel are not so pure. It may contain small metal particles itself

by the blades of a plastic granulator used to produce regrind or the metal mixing components used


in the manufacture of the raw plastic pellets. Metal particles can ruin the sleeve of the injection

barrel or the surface of the screw. Therefore, a magnet could see at the bottom of the hopper.

Magnet drawer also could see on some machines. The selection of the magnet or drawer is limited

by the machine size and purpose of the machine.

3.1.3. Injection Screw

Injection screw or lead screw is the next important part of modern day injection molding machine.

It designed in the shape of auger and placed inside the heating barrel. It plays 2 major to the

machine as, auger fresh material from the hopper area into the heating area of the barrel.

Meanwhile, mixing and homogeneously maintain temperature of the molten plastic. Other than this,

screw generates some amount of heat by the friction inside of the barrel. So, it increases the life

time of heater and machine efficiency by decreasing electrical power requirement. The friction is

created because there is just a slight clearance between the surface of the screw flights and the

inside wall of the barrel, usually only 0.008 to 0.013cm. As the material is brought forward along

the screw flights, the plastic is squeezed tighter and tighter. The friction of squeezing generates

heat.

According to the requirements the screws designed with various factors as, shapes of flights,

distances between flights, amounts of shearing action, screw tip geometries, and methods of shutoff.

Below figure 3.1 shows some screws used in injection molding machine.

Figure 2.2: injection molding machine lead screw


3.2. Clamping Unit

Clamping unit is for produce required force to keep mold close when injection process is carried-

out. Normally tons or kilo newton used to denote clamping force. According to the viscosity of

molten plastic the clamping force varies from 5 to 20 molten flow indexes. Normally the index

range 5 to 10 is low flow, 10 to 15 are average flow and 15 to 20 are high flow.

It is not as important to remember a specific flow number as it is to know in what range a material

falls: high flow, average flow, or low flow. Then, since more injection pressure is needed to inject a

low-flow material than a high-flow material, it is understood that a low-flow material will require

much more clamp force to keep the mold closed against that higher injection pressure. Simply the

clamping force can be calculate by following equation

The depth of the mold also need to be calculated with projected area if the depth D greater than 1

inch. Normally clamp factor varied . A general purpose value is 68950

𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑 𝑎𝑟𝑒𝑎 6 6 6𝑐𝑚2

𝐹𝑐𝑙𝑎𝑚𝑝 6 6 9 6 𝑘𝑁

𝑖𝑓 𝑡 𝑒 𝑠𝑎𝑓𝑒𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟 𝑖𝑠 : 𝑡 𝑒 𝑐𝑙𝑎𝑚𝑝 𝑓𝑜𝑟𝑐𝑒 . 6 6

𝑡 𝑒 𝑓𝑖𝑛𝑎𝑙 𝐹𝑐𝑙𝑎𝑚𝑝 94 6𝑘𝑁

Example question:

Find-out the clamping force for the below figure. The dimensions are l=16cm, w=16cm

and d=0.5cm. given clamp factor=68950

The machine with the closest rating for this product would be a 20000kN or machine.


The effects that could be arise by improper calculation of clamping force can be point on following

bullets

By low clamp force

Mold will not be stay close when injection process is carried-out

Final product could get flash or non-filled.

Flush creates a secondary operation and increase product cost.

By higher clamp force

Can damage the mold or press.

Molds are so cost. Therefore, it increases product price

Clamping mechanisms can damage

There are several mechanisms available for clamping unit. Hydraulic and mechanical (toggle)

systems are the famous systems for clamping unit.

3.2.1. Hydraulic Clamping System.

This system work by the force induced in hydraulic motor. Therefore, a very good efficiency and

work-force can gain from this system. Beyond this, this system allows to regulate the clamp

pressure over a wide range. Therefore, this system not only save money, but also machine and the

mold from catastrophic failures.

As there are advantages with hydraulic system, disadvantage also should be pointed. The limitation

of this system is, tonnage requirements approach the maximum rating, extreme injection pressures

may overcome the clamp force and blow the mold open. This results in flash, short shots, and

possible cycle interruption.

3.2.2. Mechanical Clamp (Toggle) System.

This system works by the knuckle and scissor mechanism to carried-out this job. A small piston is

attached a small hydraulic cylinder actuates the arms by pushing along their centerline to open the

mold. As the piston moves forward, it pulls the arms together and closed the mold as described in

the figure 3.2


The principal advantage of the mechanical system is that once it is locked in place, it is virtually

impossible to blow the mold open even if injection pressures are beyond those required. Of course,

there are limits to the pressure it can sustain, and eventually machine damage will occur if the

injection pressures are held beyond requirements for extended periods. But once the system locks,

there is no doubt that full tonnage force is available. Meanwhile, the knuckle linkages and bushes

need to replace regularly due to wear. Even if reduced this failure by proper lubrications, another

limitation is, impossible to regulate clamp pressure. For more knowledge under this heading access

sinothech-2014

4. Demonstrate a Simple Machine.

All most all the larger machinery is constructed according to small and simple principle. Similarly

this injection molding also can be manufactured through the above statement. Figure 4.1 describe a

simplified version of modern injection molding machines.

Figure 3.2: Toggle system (avplastic.com)


It is not so cost as modern day injection molding machine. Therefore, this machine worth for small

entrepreneurs, colleges…etc. further; this machine does not need larger ground area. It is just70cm,

50cm, and 35cm in length, width and height respectively. Further, low noise, low power

requirements also to be pointed when talk about this machine. Beyond all of this, cost of the

machine is the main point to denote at this moment. Cost of the machine for fabricate given on the

below Table 1

Income(LKR) Expenditure (LKR)

capital 22,000

Material 7000

Machine hire cost 10,000

Other wages 5000

Table 1: Cost for fabricate desktop injection molding machine(DIMM)

Further, the accessibility to 200oC temperature, customers are let to use several types of plastic such

as HDPE, LDPE, PP, ABS,…etc. except nylon ,Teflon…etc. therefore, the machine can used to

produce bottle lids, toys, small household items….etc.

As well as this machine for home uses, laboratories also can use this machine for find-out some

experiments such as melt flow index. So, it helps to determine flow behavior of material. A melt

flow index machine could see in figure 4.1 below

Figure 4.1: Simplified Desktop Injection Molding Machine


Due to the very less moving parts, customer not needs to pay attention as maintenances. When use

for long time, then only customer need to replace a rack and pinion. It can reduce if pasted

lubrication oils as it needed. Moreover, the nearby places of heater might get corrosion due to the

high heat. Other than that, paint pasted at the initial stage is so enough.

By the side of consumer, need to pay small safety attention. The machine is almost fully fabricated

with metal. So electric shock may affect consumer. So, users requested to wear sleepers or insulator

when work. The below figure 4.2 describes path of electric shock.

Figure 4.2: electric shock path

5. Engineering behind DIMM

Engineering is essential for construct a successful machine. Even technician fabricate, a part there

to engineers to select proper materials, correct nut and bolts, welding….etc. therefore, engineering

of this machine describe on coming several topics.

Figure 4.1: Melt flow index machine


5.1. Material Selection

This machine constructed with three types of metals as mild-steel, Galvanized steel, and cast iron.

There are several reasons for select these three types of steel all over the machine. Cost and the easy

to purchase are the main reason for the selection. Other than this machinability, weld ability and

such fabrication factors also considered when select material for this machine. Moreover, corrosion

resistance is an advantage could gain by galvanized steel. Because, several failures occurred by

corrosion. Even there are several techniques for preserve steel from corrosion, introducing corrosive

less steel will be basement for several engineering applications. Simply chemical reaction formula

for corrosion can be shown as below.

4 2 2

Even the corrosion is half to ferric level; it creates big failures in applications when use for long

time period. Therefore, paint pasted all over the machine as protecting this machine from corrosion.

The corrosion rate can be increased by following factors

Salty water

Acid

Heat

Even the salty water and acid not involved in this machine, involvement of heat cannot be

eliminated. So, special consideration needs to be offer for this machine. It can be by the following

forms

Paint

Grease

Electro plating

Keep contact with magnesium…etc.

The bullet can be continued for few more bullets. But processes other than painting are cost. So

finally decided, use mild steel because of the following reasons and protect them from paints.


Through the table 2, the properties needed for this machine is so suit with mild-steel. High carbon

steel is over design and low carbon steel not very low qualities. Therefore, mild-steel selected to

construct this machine.

5.2. Fabrication Techniques

Steels are available in the form of tubes, sheets…etc. have to shape by using machineries or

blacksmithy works to requirements shapes. Lathe, milling, drilling, shaping are the famous

machineries for this operations. Other than this, CNC, ECM machines are some more machinery

available for larger production rate. So, lathe and milling operations will be discuss on coming

chapters.

Table 2: Mechanical Properties for High, Low and Mild steels (azom.com-2015)

Properties

metric

Low carbon

steel

Mild-steel High carbon

steel

Hardness, Brinell 126 163 187

Hardness, Knoop 145 184 209

Hardness, Rockwell B 71 84 90

Hardness, Vickers 131 170 196

Tensile Strength, Ultimate 440MPa 540 MPa 635MPa

Tensile Strength, Yield 370MPa 415 MPa 490MPa

Elongation at Break 15% 10% 10%

Reduction of Area 40% 35% 45%

Modulus of Elasticity 205GPa 200 GPa 212GPa

Bulk Modulus 140GPa 140 GPa 140GPa

Poisson's Ratio 0.290 0.29 0.27-0.3

Machinability 70% 160% 60%

Shear Modulus 80GPa 80 GPa 80GPa


5.2.1. Lathe Machine

The operation carried-out by the lathe machine called as turning operations. The job is performed

by rotating the work-piece against a sharp tool. A lathe machine consist headstock, tailstock, and

carriage. Following figure 5.1 describes a lathe machine.

Headstock of a lathe is the power source for machine tool. The prime mover (motor) is usually

fitted at the bottom side and is connected to the spindle of lathe using flat or V-belt on stepped

pulleys. In modern lathes, gears are also used to get large speed variations. The spindle carrying the

work revolves inside heavy duty bearings in the headstock.

Meanwhile, the right end of the work is supported by a stationery center called tailstock. The main

function of a tailstock is to hold the dead center which supports one end of the work. Its position

can be adjusted and clamped and the bed. Figure 5.2 describes cross section of a tailstock.

Figure 5.1: lathe machine (baby lathe)


Likewise, carriage also pointed at this moment. It placed on the bed in between the headstock and

tailstock supports guides and controls the movement of the cutting tool. It consists of several sets of

parts like apron, saddle, cross slide, compound rest and tool post.

Apron:- it is the lower vertical portion of the carriage hanging on the saddle and contains the

controls for the tool movements and carriage movements. Apron contains gears and clutches for

transmitting motion from the feed rod to the carriage. The split nut mechanism which engages with

the lead screw, gives the movement of tool for thread cutting.

Saddle:- this is an “H” shaped cast frame which is resting flat over the bed. This part slides directly

over the guide-ways. The apron is hanging from the front edge of it. The cross-slide, the compound

rest and the tool post are fitted over this. Figure 5.3 gives the layout of the arrangement.

Cross-slide:- the cross-slide mounted over the saddle enables the cross movement to the tool post.

In order to move the cross-slide forward and backward, the screw fitted below it, is turned by

rotating the handle provided at the end of it. When the screw rotates, it moves through a nut which

is fitted below the cross-slide, resulting the cross movement.

Figure 5.3. Saddle of lathe

Figure 5.2: tailstock (south bend 9inch)


Compound rest:- the compound rest is fitted over the cross slide. This has a circular base to obtain

angular movements. The compound slide has a screw and nut arrangement to get forward and

backward movements for short lengths.

Tool post:- the tool post mounted on the top of the compound rest. The tool is fixed on the tool post

for cutting action. There are different types of tool post available in market. They may be

Single screw tool post

Four screw tool post

Open side tool post

Four way tool post

Below figure 5.4 describes a single screw tool post.

There are several tools can be used in lathe machine. Mostly used tools when fabricating DIMM are

pointed below.

Cylindrical turning tool

Facing tool

Grooving tool

Parting off tool

Forming tool

External thread cutting tool

Drilling tool

Boring tool

Figure 5.4; single screw tool post (cnc.info)


Emery paper

A common problem faced when work with this tools is tool sharpening. The tool bland can be

occurring by improper lubricants and incorrect cutting speed. Any liquid can be used for lubricant

purpose. But it should not be reacted with work-piece and inflammable. Because of the possibility

for fire accident is high due to generating heat on tool and work-piece by cutting process. Other

factor cutting speed of machine can be calculated through following way.

The cutting velocity of work-piece is selected by the following factors.

1. The physical property of the working material likes hardness, brittleness, ductility…etc.

2. The material property of cutting tool.

3. The feed and depth of cut

4. The rigidity and capacity of the machine tool to resist the cutting forces.

A calculation method of finding the approximate cutting speed, feed and depth of turning is given

as:

( ) 2

A table could see in lathe shop is given below for easy regarding lathe operators to find C and V

Working material V(m/min) C

Mild steel 20-28 24

High carbon steel 12-18 13

Cast iron 18-25 18

brass 45-90 48

Bronze 15-21 21

Table 3: suggested values for V and C with high speed steel cutting tool


5.2.2. Drilling Operation

Drilling operation is carried-out by drill machine. There are several types of drill machines

available today market, most of the workshop use bench type drill machine and portable drill

machines. Similarly, number of drilling tools available today. Twist drill as shown below figure 5.5

is the widely using tool. Other than this, reamers, taps, counter boring, centering, spot facing are

some more operations can be done by drilling machine.

The related calculations for drilling operations are similar to lathe operations. But, the parameters

are varies. Therefore, the equations are repeated

( )

( )

Figure 5.5: drilling job


( )

. (9

)

Correct parameters selected by using above equations when drilling operations carried-out for

DIMM. They are given below

Tool material : high speed steel (HSS)

Point angle : 1080

Spindle speed : selected according to the drill bit diameter by the

range of 3000rpm to 4200rpm

Type of bits : twist drill

Type of drill machine : bench and portable

5.2.3. Milling Operation

Milling operation for construct DIMM is very less. Mill machine is used only for fix rack of the

gear on to the shaft. Important points of milling operations are pointed as shown below.

Type of machine : horizontal milling machine

Cutting tool : end mill cutter

Tool material : HSS

Work holding method : machine vice and V-clamp


5.2.4. Arc Welding

Welding job was carried-out for several parts as joining two different individually fabricated. Arm

and the barrel, main column and base plate are some example for welded job carried-out parts.

Below symbols reveal the reasons for arc welding used for joining purposes.

Cost is low.

Wide material range (several materials can be welded).

Easy to find transformers and related accessories.

Strong when compare with other welding techniques.

As well as arc welding contains this uniqueness; the bad effect also should be pointed. Coming

bullets reveals some bad effects of arc welding.

Possibility for eye blindness is high.

High heated chips can cause some wounds.

Electric shock hazard can arise.

Following safety precautions should be taken for safe-full and successful works to eliminate the

accidents of welding.

Face shield.

Safety goggles.

Apron.

Hand gloves.

Meanwhile, K.C.Johan (p 89, 2010) reveals welding procedure on his book. He says 15 steps as

welding procedure

Figure 5.6: milling job


1. Read the given drawing

2. Carry-out edge preparation.

3. Select correct weld electrode.

4. Select the size of the weld electrode suitable to the thickness and type of weld.

5. Find the approximate length of run per electrode or the speed of travel.

6. Finalize the sequence.

7. Join the parts to be welded by C-clamp or by vices.

8. Connect the neutral or negative terminal and close the loop.

9. Select the correct current and voltages.

10. Make sure the system is ready for welding works by test on a testing material as grip. Use

hand screen from this moment on every coming steps.

11. Make tacks on certain time periods.

12. Check the alignment of the pieces of the pieces, after the tack weld.

13. Start to welding work from one end.

14. Remove the slag using the chipping hammer.

15. Inspect the defect for successful welding

5.2.5. Blacksmithy Works

Blacksmithy is a shaping method for steels and such harder materials. Any harder material get soft

when it is heated for red hot level is the basic concept for blacksmithy works. Smithy is used to

shape relatively small jobs by hand hammering. Medium and larger components are shaped using

machine forging process. In both cases the metal is heated to red hot temperature to make it soft and

plastic. In smithing the heating is done in open fire or hearth while for machine forging the metal is

heated in closed furnace. In hand forging, hand tools and hammers are used to shape metal. The

Figure 5.7: blacksmithy work


skill of the operator is the primary part to produce the required shape and dimensions. A good

producer keeps the following tools with him

1. Work supporting tools

Anvil

2. Hammers

Swage block

Bick iron


Vanier caliper

3. Tongs

4. Metal shaping tools

5. Measuring tools

Not only tools enough for blacksmithy works. When give adequate heat for work-piece, then only

the job become easy. For smithing the temperature of steel estimated by the color of the heated

zone. Dark red colour is obtained about 7000C and cherry red at 900

0C. The colour becomes orange

at 11000C and white hot at 1300

0C.

Heating of steel improves softness and reduces tensile strength resulting its plasticity and

malleability. Proper heating gives easiness for shaping and good surface finish. If the metal is

Micro-meter

Steel ruler

Figure 5.8: blacksmith tools


overheated and kept for long time in a furnace, burning due to oxidation may occur resulting cracks

on surface melting of the heat-effected zone.

Metals are with grains. Those are squeezed or damaged by hammering and such operations.

Therefore, the strength of the work-piece at bends and squeezed places are weak. There are four

heat treatment processes to neutralize or stress relief actions to the grains at bends. They are

1. Hardening

2. Tempering

3. Annealing

4. Normalizing

Hardening: hardening is a heat treatment process in which the metal is heated about 500C above the

higher critical point for mild-steels. Then the metal is held at that temperature for sufficient time to

change into austenite structure and cooled very rapidly by quenching in a suitable medium like

water or oil. This process gives the maximum hardness for the steel. Normally these processes are

carried-out for tools, dies, machine parts…etc.

Tempering: the subsequent heat treatment for reducing the hardness obtained by hardening process

is called tempering. In this process the hardened steel is reheated to a temperature below the lower

critical point, retained at that temperature for sufficient time and then cooled slowly to the room

temperature. Depending on the holding temperature range, tempering process can be classified as

1. Low temperature tempering (1500C to 250

0C)

2. Medium temperature tempering (3500C to 450

0C)

3. High temperature tempering (5000C to 650

0C)

Annealing: annealing is the process of heating the metal to a temperature that will remove the

distortion of grains of the metal and then cooling at a slower rate so that, at room temperature it has

no grain distortion or strain. Depending on the temperature, sustaining time, cooling time, cooling

rate, and the composition of metal…etc. the annealing process can be grouped as

1. Full annealing

2. Process annealing

3. Isothermal annealing

4. Diffusion annealing


Normalizing: the normalizing process consists of heating the work-piece about 500C above its upper

critical temperature and then cooling in still air at room temperature. If necessary, the metal may be

held at the elevated temperature for a short period. Normalizing differs from annealing in the sense

that the holding time at the elevated temperature is very short or zero and the cooling rate is rapid

for the process. The normalizing process removes the internal stresses, refines the grains to smaller

size and improves the mechanical properties such as impact strength, yield point, ultimate tensile

strength…etc.

Through above stress relief processes, hardening was selected. Because it is

Speed than other process.

Process is easy.

Gives maximum hardness.

5.2.6. Grinding Process

Grinding process is a metal removing process for sharpen the cutting tools and blind or chamfering

the work-piece. Here also several grinding machines developed with several techniques. Pedestal

grinding, portable grinding, center-less grinding are some example for grinding operations. Below

Figure 5.9 describes some of the grinding operation.

Grinding machines use two types of cutting tools as sand papers and grinding wheels. Mostly

portable grinders are with sand papers and other grinding operation such as pedestal, center-less is

with grinding wheels. Grinding wheels are point by following method

Xx D 150 P YY M ZZ 3

Figure 5.9: Grinding Operation


Where:

Xx :- manufactures symbol for abrasive

D:- abrasive type (diamond or cubic boron nitride)

150:- grain size (coarse, ,medium, fine, very fine)

P:- grader scale from A to Z( A soft M medium and Z hard)

YY:- concentration(manufactures designation)

M:- Bond type (B=resin, M=metal, V=vetrified)

ZZ:- bond modification

3:- depth of abrasive in mm.

But, these details cannot be finding in every grinding wheel. Shop dealers gives grinding wheels

when customer request as hard or soft grinding wheels. So, DIMM grinding works were done

medium level grinding wheels with varying hand pressure.

5. Conclusion and Recommendation

Several inventors’ initial projects were total fail. But this little project DIMM cannot say totally

failed. It means little success is hidden behind this machine. Melting plastic pallet and ejecting it to

the mold is the big goal of injection molding. The DIMM had passed the melting part, remaining

part was the big issue for this machine. It means, DIMM might be succeeded if pressed the plunger

by hand other than gear box. Due to the high compressive of plunger, at a certain level the gear get

gets slip. So this is the big issue of this machine.

Even this machined failed little amount, it helped to gain several experiences in the way of

blacksmith works, lathe works and more over designing experience. It’s the most important point

for mechanical engineers. Because, several projects could see, as over design sometimes no

engineering behind those projects may be sometimes safety not there. When compare those factors

with this DIMM, even not say 100%, just able to say around 75%. Because, DIMM had passed

following factors successfully

Proper material selection

Easiest raw material feeding

Safety ensure by separated electrical control box.

Comfortable width, height and lengths

Very good aesthetic approach as covering customer….etc.


Reference and bibliography

British plastic federation (2015). available at:

http://www.bpf.co.uk/plastipedia/processes/Default.aspx [accessed : 25th

april 2015]

Plasticindustry (2015). Available at: http://www.plasticsindustry.com/plastic-processing-

methods.asp [accessed: 20th

april 2015]

Avplastic. Available at: http://www.avplastics.co.uk/njection-moulding-history [accessed:

29th

of april 2015]

Azom.com(2000-15). Available at: http://www.azom.com/article.aspx?ArticleID=6115

[accessed: 17th

of may 2015]

K.C. John (2010) mechanical workshop practice. 2nd

edn. India; PHI learning (pvt) ltd.

http://www.bpf.co.uk/plastipedia/processes/Default.aspx

http://www.plasticsindustry.com/plastic-processing-methods.asp

http://www.plasticsindustry.com/plastic-processing-methods.asp

http://www.avplastics.co.uk/njection-moulding-history

http://www.azom.com/article.aspx?ArticleID=6115

desktop injection moulding machine

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