EXPERIENCE ON THE BENCH
Moldmaking quality is not all hardware or software. The most important area of the mold shop, according to consultant Pirro, is the bench area: "If you don’t have good quality men at the bench, you’ll never make a good mold." Dow’s Payson agrees and tries to gauge the level of experience when touring a mold shop. Payson looks for the number of master moldmakers and how they are employed. In his view, the high skill level of a master moldmaker enables him to be innovative; if necessary, he can invent a new way of machining a piece of metal. "If a shop has an experienced journeyman or master squaring up blocks for electrodes, then his time is being wasted. If the master moldmaker is spending a good part of his time teaching journeymen or apprentices and the rest of his time doing very complicated work, then his time is well spent."
According to Jerry Lirette, president of D-M-E Co., Madison Heights, Mich., mold buyers should ask about the turnover rate of shop employees. "The length of time a company has been in business and the longevity of the people in an organization is often an indication of stability and consistency in the area of product quality." Similarly, George Baldwin of Lakeland Plastics, Inc., a consulting organization in Mount Arlington, N.J., recommends paying attention to the range in age of a shop’s employees: Are they all reaching retirement are or are they all young? The former presents a long-term problem when all of the old hands are gone; the latter a current problem, because of lack of experience.
Payson looks to see if there is an internal training program in place, and would like to see more formal training of apprentices in general. That reasoning is shared by Stoll of Armin Tool, who says, "Our best toolmakers are those who have served their apprenticeship with us." Armin Tool runs a formal four-year apprenticeship program in conjunction with the National Tooling and Manufacturing Association in Chicago. Apprentices are allowed to accumulate 2000 hr per year of practical shop experience toward their apprenticeship training. After 8000 hr of experience, a graduate is considered a journeyman moldmaker. In his shop, 10% of moldmakers are considered masters.
Potential customers should inquire whether a moldmaker’s design work is in-house or farmed out, says Baldwin of Lakeland Plastics. Mold design performed on the outside could lead to inconsistent quality, depending on whom the job is given to, he says. Other things to look for are a moldmaker’s level of design experience, the CAD/CAM system, and the compatibility of his CAD system with that of the customer.
In evaluating design capability, Larry Loser, a senior program engineer with furniture maker Herman Miller Inc. in Zeeland, Mich., likes to see a certain mix of practical shop and tool-design experience, as well as formal engineering training.
Good communication between moldmakers on the bench and designer/programmers in the tool shop is important, according to Payson. "If they don’t have a good relationship, they are not going to build a good mold." In addition, he prefers that mold designers have experience either in running machining equipment or in CNC tool-path programming. "I frequently see parts designed in which a mold designer asks moldmakers on the shop floor to stand on their heads to accomplish something that could have been done more easily." He also looks for mold designers to have a working knowledge of good plastic part design practices as well as molding practices–someone who can raise a red flag if there is a missed detail in the part design, such as an inconsistency in the nominal wall thickness.
There should be good communication between the part designer and the tool designer as well, according to some customers. For example, computer maker Digital Equipment Corp. in Maynard, Mass., which buys about a third of its molds directly from toolmakers (and two-thirds subcontracted through custom molders), has focused its efforts on early involvement in the tool design. To that end, according to Raymond Vino, who is involved with product development at DEC’s Plastics Technology Group in Littleton, Mass., DEC has gone over almost exclusively to electronic data interchange (EDI) of a dimensionless database in communicating its part design to the molder and toolmaker. "I want to make sure that our part designer can talk to their tool designer, because those two folks, at the end of the day, know more about the part and tool than anyone else ever will."
Good record-keeping is important to avoiding misunderstandings when making changes in a tool design. Armin Tool, for one, documents all changes, noting revisions on the tool drawing. Loser of Herman Miller questions toolmakers on how engineering changes are documented; he wants to be sure that "ECs" are communicated to the shop floor as soon as possible.
Early cooperation between the end-use customer, molder, and moldmaker makes possible so-called concurrent or "parallel-path" engineering, which can considerably shorten a product’s time to market, according to George Freeborn, president of Textek, a custom molder in San Antonio, Texas. He says that he is participating more often in this approach, which allows some manufacturing to take place during the design phase of the project.
Given the wide range of CAD software and operating systems on the market, from PCs to workstations, customers such as DEC require some translating capability from their tooling sources. DEC’s Vino points to a trend toward 3-D solids modeling in CAD/CAM software, for which the more powerful workstation-based systems are better suited. That trend may present some difficulty in translating CAD data, because IGES lacks a mechanism for transmitting 3-D solid models.
DIVISION OF LABOR
One of Nypro’s requirements is that its moldmakers assign multiple toolmakers to each mold. This requires a systemized approach to moldmaking and a higher degree of coordination within the shop, says Rizzo, but helps ensure a higher degree of repeatability than if just one toolmaker works on each mold.
Vincent Lomax, v.p. of Tech Mold Inc., part of the Tech Group in Tempe, Ariz., notes that 10 years ago if a shop got an order for 14 molds, it would probably give each job to one toolmaker who had responsibility for that tool. When the molds were delivered, the customer would have 14 slightly different and distinct molds. "That’s no longer acceptable in a world-class environment. Today, a customer must be assured that the quality of the mold is consistent and representative of that shop’s quality, not the personality of the moldmaker."
To that end, Tech Mold divides its shop into teams, each with its own specialty. As a mold progresses through the shop, each team of "precision specialists" performs its specialized function, such as grinding or EDM, on every mold. A master moldmaker is responsible for that project and orchestrates it through the whole shop. "We are no longer in the business of moldmaking, we are in the business of mold manufacturing," says Lomax.
The approach requires a high level of communication between the various specialists in the mold shop. After the final design is completed, Tech Mold holds a "kick-off" meeting between the designer, lead moldmaker, purchasing agent, team leaders, and foreman to go through the drawings in detail and plan the job. "The reason for the meeting is that every department leader knows what’s coming, knows what the customer’s expectations are, and has input on how jobs are prepared for his department," says Lomax.
Because the mold is divided into subassemblies, a dependable scheduling system is crucial to provide a good grip on shop loading and ensure that the delivery date is met. At Tech Mold, shop loading and department loading are tracked by a computerized scheduling system, and the status of each job is reviewed once a week at a staff meeting. Job status is measured not only in number of hours spent in labor, but also in terms of the actual completion of the mold.
HOW TIGHT A TOLERANCE?
The ability to machine interchangeable components becomes critical in shops using a systemized approach to mold manufacturing. Interchangeability means that every insert should be identical and meet specifications. The concept applies to the same components within a mold or in different molds. According to Lomax, "We’ve gone as high as 15 molds over a 10-year span where every component is 100% interchangeable from the first mold to the last. Cavity #1 in Mold #1 will fit and function in Mold #15 in any cavity position."
Lomax claims the demands for ever tighter tolerances are changing the rules for what is acceptable in a world-class quality environment. One old rule that has gone by the wayside, he says, is that moldmakers can consume up to 50% of the tolerance on a critical component. "Today we are being asked to build molds to within tenths of a thousandth of an inch, and that every insert be 100% interchangeable with any other insert in the mold."
Nypro, for example, allows moldmakers only 20% of the tolerance on any critical dimension on part drawings. "If the tolerance is 0.001, they can only have 0.0002 to play with. In our own tool shop, we have only two or three moldmakers who can machine to that," says Rizzo.
Dow’s Payson looks for the ability and willingness of the shop to check the accuracy of its own machining with coordinate measuring equipment or a comparable checking device. "The operator who set up the machine may have been off 0.003 to 0.004 in. in the X-direction when they found the center of the block," he notes. Conscientious checking at every stage of the process helps to ensure that tight tolerances are kept.
According to some moldmakers, the ability to perform as much work as possible in-house helps to ensure interchangeability because it increases the control a moldmaker can exercise over tolerances. Richard Lappine, general manager of Comet Tool Co. in Williamstown, N.J., advises customers to ask moldmakers how much work is being done outside the shop. "In some cases, outsourcing is not a bad practice. But get familiar with the company’s sources. Ask the moldmaker to let you see what he’s buying and where he’s buying it."
One way to help guarantee that molds are machined to tight tolerances is to periodically calibrate the equipment. Tech Mold, for example, contracts a company to come in and calibrate its equipment once a year.
As important as calibration is, however, it’s still only a snapshot at a point in time. More valuable, says Tech Mold’s Lomax, are a regular maintenance program and employee training. The most subtle change in the mold manufacturing environment or measuring equipment may be enough to alter the process, he explains, and moldmakers must be trained to recognize that. "You need always to have checks and balances. On every job done at Tech Mold, each employee checks it to make sure it is right before handing it on to the next person. If something is out of calibration, he will surely detect it long before a calibration program finds it."
Tech Mold uses a technique called Gauge R&R to maintain the repeatability and reliability of its measuring equipment and of the individuals using them. It’s a method for determining if the gauge is consuming a portion of the tolerance, and if so, by what percentage. In this procedure, an individual checks a random dimension repeatedly on 10 inserts or gauges, and a second person documents the dimension each time. The results are put through an equation that calculates the percentage of gauge R&R that is introduced into the process by either the gauge or human measurement error. "It’s extremely difficult to get below 10% gauge R&R !when working with tolerances under 0.0005^," says Lomax.
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