The efficiency of mold changes, a common task in many custom injection molding shops, is a key factor in determining how much machine time is available. Poor performance in changeover times and approach can make or break a company with a lean manufacturing ideology. Efficiency, consistency and speed are three primary focuses in a lean-minded shop. This article points out some of the principles of NASCAR race teams and how these can be implemented into a molding shop's mentality to drastically reduce changeover times and the downtime associated with mold changes.
|Image courtesy Junior_at_Darlington.jpg: U.S. National Guard.|
Lean approaches in plastics injection molding are a vital requirement to the success of any molding operation. Efficient molders can cut their costs and consistently undercut the quotes of their competition. Companies that successfully implement "lean" into their operation do so through:
- Fast and consistent changeovers;
- production runs with minimal start-up scrap and minimal-to-no scrap during the run;
- ongoing continuous improvement projects aimed at all facets of the molding operation;
- standardization of mechanical components and procedures;
- and development of strategic, consistent approaches that streamline the overall time and consistency of downtime as it relates to the time associated with the end of a job, mold changeover and the transition into a new job start up.
By following some of the lessons of a NASCAR pit crew, a plastics processor has the opportunity to eliminate inconsistency and downtime associated with poorly planned changeovers. The first step is to meet with the set-up team, evaluate each job individually and then establish a solid, streamlined approach toward downtime associated with job changeovers.
Let's consider some of the parallels between a NASCAR pit crew and a mold set-up team. Each has the responsibility of maintaining and servicing a machine, and each can ultimately affect the success or failure of the operation he or she is responsible for through poor performance and approach. Each member has a common goal—the success of the operation. And in most cases each one takes great pride in its contributions to that success.
Clearly, there are some strong similarities between both teams, despite the vast difference between the machines for which they are responsible. By inputting NASCAR-style techniques into your mold changeover approach, you can get similar and cost-effective results through faster change times and improved consistency through standardization. Mold changeovers are very similar to the pit-stop scenario. In NASCAR, the car is directed to stop in a couple of laps as the pit crew prepares for the event. A plan is developed based on the needs of the car. The crew knows well in advance what its duties are, and each member is provided with the necessary tools and training for a quick response. Poorly organized teams find themselves overwhelmed and sluggish. A properly prepared and trained team that performs the stop quickly and efficiently secures the win.
Successful mold changeover is no different. The team knows in advance what the change requires and has developed a successful approach through proper planning and preparation. This helps to identify the procedures that need to be performed in a step-specific manner. A clearly defined guideline establishes precise actions and couples them with the proper tools to perform the task quickly and with repeated accuracy. Tools needed to make a mold change fast and successful are best identified by a complex review of what each step of the changeover requires and whether improvements can be made. Aggressive changeovers are groomed, not spur-of-the-moment accidents.
Ready, set, set up
Here are some of the techniques that can be implemented into your operation for optimized set-up performance.
Time study: Successful pit crews have a very lean approach. Through carefully meditated actions, they optimize the speed and accuracy of the pit-stop events for which they are responsible. Perform a time study on your mold changes. Time each move that is made by the set-up crew, and document the task performed. Time study is not an event that is applied only to a single job and then carried over haphazardly to every other operation. Molding operations each have their own distinct character and requirements. Review each job individually, and develop changeover plans that address every variation. Every changeover has a unique set of procedural challenges. Identify what steps are required to quickly and consistently replicate the changeover. By developing a clear and concise pattern, the transition becomes easy to reproduce and prevents potential failures that are a common result of poor planning and inconsistency.
Once this has been completed, gather the entire set-up crew and evaluate what can be improved. Can some steps be removed from your changeover? Can some steps be combined or be performed at a different time to remove waste-of-motion from the changeover time? Once your team finishes evaluating the set-up procedure, and wasted motion has been removed from your set-up approach, document and implement the optimized changeover approach. Utilize the skills and knowledge of everyone associated with the changeover event to ensure that every benefit and drawback has been addressed and properly planned for. Remember: There will be different tasks required as you develop your overall production plan. If you have five different jobs that run in a specific press, every scenario has to be individually evaluated and planned.
Now that you have a "lean" changeover, it is time to implement it across the company and across shifts to ensure that a standardized approach will be in effect. If one crew performs the same change with even the slightest variation from the planned event established by the team’s changeover development plan, the result can be catastrophic. For example, suppose that one crew consistently utilizes the correct nozzle tip, while another team has not been trained to consider its importance. The technician may face a totally different molding result requiring varying processing results and the potential for an increase in scrap. It is vastly important to develop a very specific approach that is clearly communicated and embedded into the set-up procedures via training and oversight of all personnel.
Quite often the set-up crew will find itself feeling awkward at first. The end procedure is a compilation of the insights and development of the group as a whole. Through collaboration and planning, the team is able to eliminate waste and poor time management through a collective assessment by all members responsible for the production changeover. As the team gains experience and speed through repeated changeovers, it will see the benefits. By removing inconsistency from changeovers, a company gains better control. Engineering the steps taken for mold changes into a repetitive event will improve the set-up team's ability to perform faster and with better accuracy.
Tools and equipment: NASCAR teams are given the tools they need to make fast and accurate changeovers and to service the machinery for which they are responsible. The same needs to be true for mold-change teams—a crew with the proper tools will greatly outperform a team that struggles to find the tools and equipment it needs to effectively perform its job.
New technology and approaches should continuously be researched for optimization. As new tools are introduced into the shop, proper training in their use needs to be applied to ensure they are effectively employed.
Standardization: Bushings, mold thickness and mold width should be standardized whenever possible to reduce lost time due to mold height changes, tip changes and resetting clamp placement to accommodate mold-width changes. Shuttles, hydraulic clamps and magnetic platens are more expensive alternatives to fast changeover clamping, but are not always economical for a smaller facility handling parts that are dimensionally and visually less critical. For the small molder, planning your changeovers and modifying your tooling can be a better alternative.
Whenever possible, reduce the number of tools required to perform the tasks at hand. Fewer tools require less searching, and they are more effective because of frequent use. If a company utilizes a shared toolbox, 5S the box using hard foam with tool locations cut out and clearly identified. Once tool locations are memorized, the concept of "searching" is eliminated and your personnel will just go straight to the item needed to perform a job. Regularly review the box to ensure that lost tools are replaced and that all tools are in satisfactory condition. Your set-up crew members can only perform their job to the best of their ability if the tools they use are always available and in good condition.
Water and tooling: Water-cooling connections add a great deal of time to your mold changes. Consider mounting hard-plumbed manifolds to your mold with single supply and return line hookups. If this is not economically feasible for your facility, you still have the option of color-coding your mold, water lines and manifolds to improve set-up efficiencies. In addition, tooling needs to be clearly identified to eliminate thought from changeover. Not only can your water throughput be identified, but circuits can be defined by color, as well.
Make sure that fittings and clamp bolts are maintained and replaced as they wear to prevent wasted motion trying to install defective components. Tooling should be located near the press, whenever possible, and should be clearly identified for fast discovery. Assign and document tool locations to eliminate searching for molds prior to mold change. Hoses need to be in good condition and free of damage.
Planning and preparation: NASCAR pit crews are given fair warning in most cases as to what is going to take place during the stop before the car rolls into pit row. This gives the team time to evaluate what tools it needs, what needs to take place during the stop and how to most effectively get the race car back on the track. The same approach needs to be implemented into your changeover plan.
Most changeovers can be prepped long before the change happens, and doing so will improve your set-up times. Here are some tips on things that can be done to improve changeover times through preparation.
- Place the mold to be installed near the press to reduce waste of motion. Locate the hoist near its mold extract position, so that it is ready to be quickly attached to the eyebolt.
- Plan your material changeover approach to ensure it happens quickly and smoothly. If a grinder is to be used at press side, clean it just prior to the beginning of the changeover so it is ready and in place at start-up. When using a press-side hopper, it can be cleaned and the next material loaded one hour prior to the mold-change event. Most dried materials can be run out of a barrel for one hour prior to the mold change to allow the material handler to prep the hopper and have the new material ready long before the mold change occurs.
- When the new mold requires more waterlines than the mold in production, have the water lines at the press. Inspect the new lines for signs of wear to prevent wasted effort during installation.
- Compare mold widths to determine your clamping approach. If extra clamps will be needed, have them at the press prior to tooling changeover. Review the mold for potential standardization to eliminate the time associated with die-height adjustment.
- Keep detailed documentation of what is required to perform each mold change in your facility. This speeds comparisons to ensure mold preparation is a smooth and simple task. Nozzle tip, knockout length, auxiliary equipment and operator station layout should be included so that all required equipment and tools can be pre-staged near the press prior to the mold change. Continuously review the potential for time reduction through equipment upgrade or area-layout modifications.
- Purge the press and change the barrel and thermolator temps at the start of the mold change. This allows the adjustments to settle in prior to the end of the mold change. You can also heat soak a hot-runner mold toward the end of a production run, so the hot runner will be near temperature when it is set and the hot-runner connections are reinstalled and energized.
These are just a few examples of how a facility focused on lean manufacturing can improve its set-up efficiencies and reduce downtime. Each company is different when it comes to the materials, tools and equipment that are common to its production requirements. Utilize the experience of your set-up crew to determine what problems are hindering set-up efficiencies, and then develop a plan to remove all negative elements through tools, equipment, approach and training. Regular meetings with your set-up crew help to identify what criteria and tools hamper its ability to quickly and precisely perform the changes for which it is responsible. Failure to recognize the importance of this is no different than a NASCAR team not understanding the importance of pulling a car into the pit as a race unfolds.
In closing, always understand the importance of continuous improvement to mold changes and job changeover. Continuous improvement is a vital asset to the overall performance of your operation. Develop a strong foundation for your changeover team by using its experience to develop a solid work procedure and give it the tools it needs to be efficient. Then re-evaluate the revamped system to tweak out the bugs and look for other things that can be improved. Analysis, planning, approach and re-evaluation are the keys to success for any company’s changeover plan.
Garrett MacKenzie is the former owner and editor of www.plastic411.com. Mackenzie started in plastics at the age of 19 as an operator, eventually moving up through the ranks to engineering over a 29-year timeframe. He currently works as a plastic injection consultant in engineering and training capacities. He can be contacted at [email protected].