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Copyright © 2021 by Dr. David M. Anderson, P.E., fASME, CMC
To be successful at designing products for lean production, build-to-order, or mass customization, product development teams must proactively plan product portfolios, design products in synergistic product platforms, design around aggressively standardized parts and raw materials, make sure specified parts are quickly available, consolidate inflexible parts into very versatile standardized parts, assure quality by design with concurrently designed process controls, and concurrently engineer product platforms and flexible flow-based processes.
Further, product development teams need to eliminate setup by design by specifying readily available standard parts and tools (cutting tools, bending mandrels, punches, etc.), designing versatile fixtures at each workstation that eliminate setup to locate parts or change fixtures, and making sure part count does not exceed available tool capacity or space at each work station.
Finally, products must be designed to maximize the use of available
programmable CNC fabrication and assembly tools, without expensive and
time-consuming setup delays.
For lean production, build-to-order, and mass customization, product portfolio planning must expand its focus to ensure that products are developed in synergistic families that can be produced on-demand on flexible lines.
To accomplish this, product families need to be structured so that all products use standard parts on the same flexible equipment without setup delays.
All the products within a flexible line B and possibly all the products within a flexible plant B must be compatible with respect to part standardization, raw material standardization, part/material availability, spontaneous supply chains, modularity, setup elimination, and flexible processing including CNC machine tool operation.
Older generation products may not be compatible with flexible production lines and thus may have to be dropped, outsourced, redesigned, or, at the minimum, have material substitutions. Old products worth saving may have to be redesigned or upgraded and be added to the list of potential product development projects and activities.
The evolution of product portfolios needs to be coordinated with
implementation efforts for lean production, build-to-order, and mass
customization. Decision making should be based on total cost and contributions
to the overall business model.
For lean production, build-to-order, and mass customization, products need to be designed so that:
$ All the parts can be distributed at all points of use, which is accomplished by designing around standard parts and materials from aggressively standardized lists. Too many parts would either clutter and confuse the work areas or force the parts to be kitted for a batch of products to be made, which is contrary to the one-piece flow of all the flexible paradigms. An important aspect of part standardization is fastener standardization, which is usually the easiest to do and can provide significant benefits. If screws can be standardized to one type at each work station, then autofeed screwdrivers can be utilized, which automatically orient screws and feed them through a flexible hose to a powered screwdriver. Of course, in order to designate a single type of fastener at each station, the design team will have to be concurrently designing the entire production flow.
$ Products and processes need to be designed so that there will be no significant setup for any part or product in the family. This includes any setup to (a) find, kit, load, or replace parts or materials; (b) change and position dies, molds, or fixtures; (c) change tools; (d) load, position, clamp, or calibrate workpieces; (e) adjust machine settings or calibrate machinery, or (f) change equipment programs.
$ Equipment programs can be located and downloaded instantaneously and manual instructions can be found, displayed, and understood quickly.
$ Parts and materials have been chosen so that they can be resupplied spontaneously. This includes specifying readily available parts and materials, designing around aggressively standardized parts, and specifying raw materials to be cut on-demand from the same standard input stock sizes.
$ All parts can be pulled
quickly into assembly on-demand. This includes specifying suppliers who can
build parts on-demand or working with in-house manufacturing to establish
Standardization of parts is the most important design contribution to the feasibility of spontaneous supply chains. Aggressive standardization can enable the easiest technique of the spontaneous supply chain: steady flows of very standardized parts and materials. If there are too many different parts and material types, steady flows cannot be arranged because of the variety and unpredictability of demand. The total cost value of standardization and its contribution to the business model should motivate engineers and procurement organizations to implement such aggressive standardization.
Most part proliferation happens because engineers do not understand the importance to supply chains and operations and, even if they did appreciate this, do not know which parts are best to choose. The effective procedures presented in the standardization article show how to generate lists of standard parts and materials.
The usual operational mode in a part-proliferated environment, is to order
the parts ahead based on forecasts, either for scheduled batch production or to
have forecasted parts available for on-demand assembly (the Dell model). If part
variety is truly unavoidable or parts are to be mass-customized, then they can
be built on-demand using principles presented articles, Build-to-Order
for standard parts and Mass Customization for customized
An important task in concurrent engineering is to specify not only the functional specifications of materials but also the order size and how they get cut into various parts. One company that made sheetmetal products previously ordered 600 different shapes of sheet metal, which was a logistics nightmare. The author advised them to convert to just a handful of standard types which were then cut on-demand as they were needed. Even better would be to cut sheetmetal on-demand from a coil.
Another way engineers can reduce material variety is to specify a single tolerance or grade, instead of multiple grades. As pointed out in the Standardization article, any perceived cost increase of shifting all materials to the higher grade will be more than compensated by the total cost savings and value of the business model.
Families of parts should be designed so that every CNC machine tool uses the absolute minimum of raw material types, hopefully just one so there are no setup delays to change materials.
Multiple lengths of linear materials can be obtained by ordering reels or long lengths of materials, which are then cut to length on-demand.
Inflexible raw parts, like castings, extrusions, custom silicon, and bare
printed circuit boards, should be consolidated into very versatile parts
that can be used for many functions on a wide range of products. Programmable
chips should all be programmed using the same
A spontaneous supply chain depends on readily available parts and materials. Therefore, it is an important aspect of engineers= jobs to specify parts and materials that are readily available. Usually, design engineers choose parts based on functionality and hopefully quality. But for flexible operations, availability is equally important.
Parts and materials that can be obtained from multiple suppliers tend to have better available, in general, and are also more likely to be standard. On the other end of the spectrum, parts and materials available from only a single source may some day be hard to procure at all. On the lecture circuit, the author found one company whose parts had become obsolete before the product was even released!
Rapid delivery is important for flexible operations, so design teams should specify local suppliers who will be able to supply materials on-demand. Many companies preclude the ability to obtain parts and materials spontaneously by buying from supposedly A low cost@ suppliers from another continent; see Outsourcing article. Womack and Jones, writing in Lean Thinking summarize it succinctly: A Oceans and lean production are not compatible.@ They go on to say that smaller and less-automated plants close to assembly and markets will yield lower total costs, considering the cost of shipping, the inventory carrying costs, and the cost of obsolescence when products built weeks ago no longer satisfy customers. Similarly, even local low-bidder suppliers probably are not going to be able to deliver on-demand and will most likely not have adequate quality either.
The guiding principle is to select parts and material to be readily
available, delivered on-demand, and the lowest total cost, which includes
material overhead, ordering, expediting, routing shipping, expedited shipping,
incoming inspections, kitting, internal distribution, and all the costs of
locating alternate sources of supply to counter availability problems.
Part Setup. Product design has a profound effect on part setup. Excess proliferation of parts complicates internal part distribution and may make it impossible to have all parts available at all points of use. Even a moderate excess of part types will cause setup delays to distribute, find, and load parts into manual or machine bins. A greater excess of part types may make it necessary to kit parts for every batch, which is a significant setup. Part A prep@ (such as cutting or bending leads on electronic components) is another setup that can be avoided by using versatile equipment or specifying parts that are already prepared properly for the product and the processing equipment.
Fixturing Setup. Designers can eliminate fixturing setup by designing parts for versatile fixturing which, if not already in place, may have to be concurrently designed with the parts.
Tool Setup. Designers can eliminate tool change setup by designing parts around common tools (cutting tools, bending mandrels, punches, etc.), ideally one tool that never has to be changed. If multiple tools are required, designers must keep tool variety well within tool changing capacity for the whole product line.
Instructions. Designers need to work with manufacturing engineers to
concurrently develop simple assembly procedures that can be understood in a few
seconds either on a computer screen or on paper instructions that can be quickly
located and understood.
A wide variety of machined dimensions (for mass-customized or standard parts) can be performed quickly and cost-effectively using a combination of CNC machine tools and parametric CAD, which stretches A floating@ dimensions and then automatically creates CNC programs as they are needed by CNC machine tools.
Universal parametric A templates@
can be created ahead of time for families of parts and structured so that, when
the customized dimensions are plugged in, the drawing transforms into a
customized assembly drawing which automatically updates customized part
Computer numerically controlled machine tools (hereafter referred to as A CNC@ ) offer vast opportunities to eliminate machining setup. CNC machine tools include metal cutting equipment (mills, lathes, etc.), laser cutters, punch presses, press brakes, printed circuit board assemblers, and basically any production machine controlled by a computer. Designers need to understand enough about CNC operation to use the versatility of CNC to eliminate setup.
Grouping parts. The first step in designing for CNC is to structure compatible groups of parts to be processed in each CNC machine B this was originally labeled group technology. Of course, this must be based on the overall manufacturing strategy and flow of parts and products. This evolves from a serious concurrent engineering activity in which the grouping and flow of parts are a key element of the design team= s responsibilities. The grouping may determine the type of CNC needed, or existing machine tools may specify the grouping.
Understanding CNC. After thoroughly understanding of the range of parts to be made by each CNC, the designers will need to understand the capabilities and limitations of the equipment. This can be accomplished by studying the equipment specifications and talking to CNC operators. In fact, the CNC operators should actually be on the design team to optimize the design and processing plans. Of course, the ultimate understanding would come from actual CNC operational experience, either through prior work or a job rotation program.
Eliminating CNC setup. The versatility of CNC provides unique opportunities for eliminating setup if parts are designed properly. Ideally, all operations should be able to be performed on one machine in a single fixturing, as recommended in Guideline P10 in the Design for Manufacturability article. Multiple machines will require extra fixturing setups. Even if multiple specialized machines have higher speed ratings, the total flow time through all operations including setup is what is important. The value of eliminating these setups may justify a more sophisticated CNC, compared to more setups on many cheaper machines.
In order to process parts in a single fixturing, designers need to specify a suitable datum, from which all dimensions are referenced and which is suitable for clamping to a milling machine table or lathe chuck. The part also must be designed so that all the operations can be done in this fixturing. If all operations cannot, it is important that the most critical dimensions are cut in the same fixturing, which will routinely achieve the best tolerance of the machine tool, usually +/- .001" or better. However, removing a part to reposition for a subsequent cutting lowers accuracy of these critical dimensions because the tolerance will then depend on the accuracy of the second positioning, which is usually much worse than machine tool accuracy.
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