From Donnelly Custom Manufacturing

Mold set-ups are an unavoidable part of injection molding. During this process, the molding machine is shut down for a period of time while the mold is changed. Oftentimes, however, set-ups are poorly handled, and as a result, machines sit idle far longer than they have to. What's more, an error-prone set-up can lead to sluggish cycles, high scrap rates, tool damage, flawed parts, rework, an unsteady process and delayed product delivery. Shops could even erase their entire profit margin on the job as a result of a flubbed mold changeover process.

So how do you avoid all these negatives? Minnesota-based Donnelly Custom Manufacturing believes that the answer lies in focusing on refining the mold set-up process instead of doing it perfunctorily. And so far the company's approach has yielded impressive results: it has halved mold-change times over the last two years - a huge plus for the firm because of its focus on short-run manufacturing, where an additional 10 minutes setting up could wipe out the profit on a run shorter than 2 hours.

Here are some tips from Donnelly on how you can steer clear of common mold set-up mistakes and perfect the changeover process:

Pointer #1: Pre-stage the next mold to reduce idling
Instead of waiting for the molding machine to finish its current run, let the changeover crew perform some of its duties while the press is still in production. In particular, the crew should pre-stage the next mold set-up while the press is still working on the previous mold. A set-up cart is especially handy for this purpose. It should hold all of the tools that the team is going to need to remove the previous mold and to set up the new one, including torque wrenches, impact wrenches, mold clamps and bolts, nozzles, cleaners, etc. A crew member should check that all the necessary tools are in the cart.

The crew should also schedule and stage material before the molding machine completes its last cycle. Neglecting to do this could cause a press to stay inactive for a much longer period than the rest of the changeover activities put together. For example, many materials need to be pre-dried for 2 to 6 hours before processing. Pre-staging alone helped Donnelly cut its average changeover time by as much as 33%.

Pointer #2: Clearly label and organize molds
Molders can avoid wasting time on locating and retrieving molds by organizing storage. First, they should store and inventory molds so that they are easy to find. And second, they should make sure that they position the storage close to the press for quick and easy retrieval. Donnelly accomplishes both of these goals through "mold grandstands," storage structures that look like bleachers in high school gyms. Standing adjacent to the press, these grandstands hold clearly numbered molds, which is each assigned a spot on a certain rack. The molds that are most often run are placed in the most accessible areas. An overhead crane conveys the molds. While small- and medium-size molds are kept in two separate grandstands, the larger molds are placed on a vertical racking system close to the large molding machines.

Pointer #3: Develop a checklist
Without an established process for mold changeovers, molders may prolong the set-up process as well as introduce other inefficiencies to their operation. It's key to create a checklist detailing the tools and procedures for mold attachment to the press to eliminate the possibility of missteps. At Donnelly, these checklists help production supervisors ensure that each scheduled mold set-up is performed on time. In addition, these lists allow personnel to evaluate and analyze every changeover and pinpoint areas for improvement. In fact, Donnelly went as far as writing an instruction manual for each of its molds, including the inspection of job runs for any signs of process problems.

Pointer #4: Train more people
Mold set-ups can also take longer simply because not enough people in the shop know how to conduct a mold changeover. Even small molding shops sometimes have several machines simultaneously requiring a changeover, yet many molders continue to have only one or two specialists. To prevent situations in which presses are allowed to stay idle because specialists are too busy to get to them, shops should train press operators to perform mold changeovers. Donnelly, for example, has provided changeover training to 40% of its hourly personnel. This has allowed set-ups to be performed on schedule and with greater speed as press operators are able to assist in all steps of the process. Furthermore, Donnelly has found that two-person teams are particularly effective, regardless of the size of the press. Team members have predetermined duties and work on each side of the molding machine.

Pointer #5: Communicate constantly
Regular communication is key because of the unpredictability of production schedules, which could change without notice, leaving molders rushing to work out last-minute details right before a press has to be set up. To avoid this situation, molders should hold production meetings everyday. At Donnelly, cross-functional teams convene daily to review the schedule, talk about concerns and evaluate priorities and resources. These constant discussions help to pre-empt and reduce unexpected problems throughout the operation, including mold set-ups. Moreover, these meetings allow for the exchange of ideas, which paves the way for process improvements.

Pointer #6: Don't forget maintenance.
Molders often make the mistake of neglecting equipment maintenance. This oversight can lead to equipment problems - from a busted ejector pin, to a damaged bolt hole on a platen, to a threadbare check ring - all of which could protract the process of setting up a mold.

Lessons learned
By sticking to these guidelines, Donnelly is able to execute many changeovers for smaller presses in under 30 minutes and for its biggest presses in less than 2 hours. And by following these tips, your company can certainly benefit as well.

Source: Avoid Common Mold Set-Up Mistakes
Dave Lamb and Brad Andrist
Plastics Technology, July 2003
http://www.plasticstechnology.com/articles/200307ts1.html