sergio antonio salvi, design for assembly (lecture extract)
TRANSCRIPT
DESIGN FOR ASSEMBLY (DFA)
Sergio Antonio Salvi
PRODUCT DEVELOPMENT
DESIGN FOR ASSEMBLY
Principles
■ Almost always the architecture of a product consists of more than one part (although “monocomponents” seldom can be developed as well; even if sometimes they need packaging…), so that is inevitable to develop products whose construction needs assembly processes. This technological “chapter” is important both technically and economically.
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
Scenery
■ Contrary to what inexperienced assume, assembly processes take place very frequently resorting to manual procedures, except for objects made of several hundred thousand units per year and in special cases (circuit boards etc.); it follows that the economic impact of assembling processes may be significant, depending on the labour cost, that can vary by about two orders of magnitude!
(→□)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
Scenery
Assembling by means of automated processes can be far convenient…
(robots while welding cars bodies, BMW)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
Scenery
… anyway not always possible or convenient
(NASA “Curiosity” Mars vehicle during the wheels mounting)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
DFA advantages
Designing a product according to the methodology Design for Assembly obviously determines assembly’s costs reduction, but also other advantages, so altogether:
■ assembly costs reduction (as mentioned);
■ components reduction;
■ production processes simplification;
■ support’s costs reduction.
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction
From the design point of view, the assembly’s costs reduction can be implemented in several ways, possibly by adopting analytical methods, such as those developed by Boothroyd and Dewhurst (also available in the form of software). The cost reduction strategies include:
■ 2.2.1 components reduction (as mentioned);
■ 2.2.2 parts “integration”, where possible and convenient;
■ 2.2.3 assembly operations simplification;
■ 2.2.4 if possible, encourage the "do it yourself“ assembly.
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.1 components reduction
By the work of Boothroyd and Dewhurst results that the most important parameter is the “theoretical minimum number of parts”, which leads us to estimate whether a component should, or not, to be distinguished, determining, or less, the increase of the pieces.
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
The answer to the problem derives from the following questions:
■ 1- component must move respect to others (therefore determining a “kinematic” system)?;
■ 2- component must be separated for any reason, for example related to upgrading, adding-on, wearing, consumption, reuse etc.?;
■ 3- component must be made of a material other than contiguous parts?
■ Logical that the negative response to the above questions certainly determines to resort to integration, reducing the number of components.
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.1 components reduction
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.1 components reduction
A product like this safety razor is not conform to the aim to minimize the number of the components, hence it hypothetically needs a new approach targeted to “integration”
(Gillette “Proglide”)
“Integration” strategies are explicitly dependent on the previous analysis (cf. 2.2.1 “components reduction”), and they are the obvious consequence. Almost always the integration involves the use of technologies that enable the manufacture strategy so called "net-shape“ (whose aim is to integrate into a single moulding “shot” as many “functions” as possible ), that is typical in the case of moulding processes.
(→□)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.2 parts “integration”, where possible and convenient
The benefits are significant:
■ integrated parts do not involve assembling;
■ “multifunctional” derived component is frequently less expensive, even in the case of integration of parts already “net shape" (a mould is less expensive than two, processing time is reduced, wasted components as well etc.);
■ geometrical quality is increased, furthermore the “coupling problems” are canceled.
Note that it may sometimes happen that the inverse operation –the "disintegration" of the components–, can get advantages, as in the case the design approach aims to the “modularity” (in the case, it is important to know that modularity can cost).
(→□)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.2 parts “integration”, where possible and convenient
OMITTED
Assembly operations consist of manipulation of parts so that they are quickly and correctly positioned and locked; we distinguish the “handling operation” in the following stages: holding, orienting, positioning, locking; logically, these stages are implemented according to trajectories.
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification
TIP
BALL
TANK
INTERFERENCEFITTING
INTERFERENCEFITTING
SCREWING
HANDLE/CASING
STOPPER
INTERFERENCEFITTING
PROTECTIVECAP
INTERFERENCEFITTING(DOUBLEPOSITION)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:2.2.3 assembly operations simplification
“Fish bone” diagram of assembly flows (example of a ball pen)
Blue text and black vectors: components Red text: assembly techniquesGray vectors: groups of components
TIP
BALL
TANK
INTERFERENCEFITTING
INTERFERENCEFITTING
SCREWING
HANDLE/CASING
STOPPER
INTERFERENCEFITTING
PROTECTIVECAP
INTERFERENCEFITTING(DOUBLEPOSITION)
A component is suited to DFA when:
■ 1- it is inserted from above (“assembly along the Z axis"): it is not necessary to manipulate another piece more bulky and heavy; the force of gravity contributes to the coupling; operator visually inspects the parts (“optical lines” aim to the coupling place);
■ 2- it is self-aligning: the coupling of components is facilitated by flares, pins, centering elements (chamfers, fillets) etc.;
■ 3- it does not require orientation: it must assimilate as much as possible the spherical geometry; with respect to this feature, the geometries that, in order, most respond to requirement are: sphere, cylinder (shaft, pin etc.), dual cylinder diameter (screw), double diameter cylinder with rotary locking (tongue, key etc.);
■ 4- it requires just one hand to be manipulated: a piece that offers a simple "sure grip", small, light is assembled more quickly without the need for “handling devices” such as special handles, hoists, balancers etc.
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification
■ 5- it should not be locked using tools: the use of tools greatly complicates the assembly –just think of the insertion of screws– therefore you should avoid, if possible, mechanical connection elements like snap rings, cotter pins, springs, “threaded” parts etc.
■ 6- it involves a single linear movement: a piece that is coupled with a simple trajectory is clearly more effective from the point of view of DFA: for example an “embedded” pin in place the same screwed up;
■ 7- it locks immediately once positioned: from this point of view we should avoid threaded couplings, not instant adhesives etc., especially for the fact that between the positioning phase and the locking phase, because of the time lag, the components can be in a critical situation.
In order to make easier specific assembly operations, over time many mounting components, known as “fasteners”, have been created.
(→□)PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (chamfers, as well as fillets and flares, help to make a component “self-aligning”; in the picture a couple of mechanical components suitable to be coupled)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (screws, even if always affordable and often irreplaceable, are not ideal connecting elements, from the DFA point of view, because of the critical handling; in the picture “self-threading” screws)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (pins are better than screws, if the action of the latter are not necessary)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (“tongues” and “keys” are not ideal as DFA assemblying components, anyway, because of their characteristics, sometimes are irreplaceable)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (“snap rings” should be avoided, because of the need to use special tools and their dangerousness; in the pictures: internal snap ring handling, internal and external snap rings)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (“cotter pins” should be avoided, because of the need to use special tools)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (“fasteners” have been invented to make easier specific assembly operations)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification (“snap fits” should be used, because of their perfect compliance to DFA philosophy; if “reversible” they are also in accordance with LCD strategy); furthermore they can be designed to be directly operated by the user
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.3 assembly operations simplification in a “safety razor” (“integral hinges” and “interference pins” in this product represent an almost perfect example of DFA application; furthermore being a “self-packaging” product, it is also in accordance with LCD strategy)
■ What seems an unscientific approach, related to the "modelism“ hobby, in reality it may be, in some cases, surprisingly convenient: it is a methodology that can meet the end user's favour, since it may be willing to assembly the product if, in change, it gets the benefit of easier transport from door-to-door and at a lower cost; the company who more practice this “philosophy” is Ikea.
(→□)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.4 if possible, encourage the "do it yourself“ assembly
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.4 if possible, encourage the "do it yourself“ assembly (Ikea’s packs can be easily taken home, saving money)
■ This choice must not mislead into thinking that the manufacturer is free from problems inherent to the assembly: it must provide for the preparation of the package by providing all the necessary materials (especially mechanical connection elements that do not require the use of special tools) as well as by providing components, special preparations (parts “housing”, holes etc.) and making a clear installation manual accompanied by drawings and schemes.
(→□)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.4 if possible, encourage the "do it yourself“ assembly
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
2.2 assembly’s costs reduction:
2.2.4 if possible, encourage the "do it yourself“ assembly (“do it yourself” strategy involves connecting parts, tools and instructions preparation)
DESIGN FOR ASSEMBLY
DFA and “automatic processes”
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
“Strongly automated transformation processes”, like plastic injection moulding, are very adherent to Design for Assembly strategies: that because they avoid to use manpower, determining the product quality increase and costs decrease.
DESIGN FOR ASSEMBLY
DFA and “automatic processes” (“insert moulding” tecnique)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
DFA and “automatic processes” (“insert moulding” tecnique)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
DFA and “automatic processes” (“in-mould decoration” tecnique)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
DFA and “automatic processes” (“multi-component moulding” tecnique)
PRODUCT DEVELOPMENT
Sergio Antonio Salvi
DESIGN FOR ASSEMBLY
DFA and “automatic processes” (“multi-component moulding” tecnique integrated with “insert moulding” tecnique)
OMITTED