Shop design is as subjective a topic as the tools in a craftsman's box. Past experience and personal preference are the main ingredients to a floor plan that is normally dictated by the space you have been allotted and the machine tools and other equipment you have to include into the layout.
Over the next couple of articles I will discuss different areas of concern and the impact they have in affecting mold maintenance efficiency.
When determining repair shop space requirements, the first thing to do is to establish as closely as possible, the amount of work or number of molds the shop will see in a week's time, and projected growth. The type of product molded, physical mold size and MPP (mold pull pace) will help with shop design and ancillary requirements.
Then it must be determined, again as closely as possible, how many of these molds will be long runners requiring full C/Rs (clean and repair) or wipe-downs (short, two hour runs etc.—the latter greatly reducing the time the mold spends on a bench).
In a survey of captive mid-western shops, the average number of molds pulled and set (scheduled) during a five-day week was one per press, per week. The average number of presses was 20. Unscheduled mold pulls can add another 20 to 40 percent to this total—meaning the shop will cycle some 20 to 30 molds per five-day week through the shop.
|Type of Company||Active Molds||Presses||Ave. Mold Cavitation||Ave. Daily Cavity Count||Ave. Daily Pulls/Sets||Ave. Daily Cavities to Maintain||Dedicated Repair Techs.||Shows Approximately how much work a technician needs to complete in a day to keep up.|
|Closure||500||50||32||1600||4||128||10||12.8 Cavity Mold|
|Electronics||125||125||48||6000||7||336||20||16.8 Cavity Mold|
|Automotive||35||35||4||140||11||44||6||7.3 Cavity Mold|
|Personal Products||13||13||8||104||30||240||5||48 Cavity Mold|
|Sample||20||20||32||640||5||128||4||32 Cavity Mold|
|Other "Pull Pace" Considerations|
|Documentation Practices||In-Press Servicing Requirements||Engineering Support||Mold Size and Complexity|
|Cavitation Goals||In-Press Insert Changes||Personnel Experience||Back-up Molds|
Based on this pace calculation, we will discuss a shop geared to handle the workload of cleaning and repairing approximately 25, 7,000-pound (maximum), 32-cavity molds each week.
The pace chart will show how much work is required of each repair technician (yellow) to keep up with scheduled mold pulls (blue) based on average mold cavitation (purple) and number of repair technicians (green).
According to the chart, the MPP of our sample shop would require a minimum of four repair techs to clean and repair at least one 32-cavity mold each per an eight-hour day. This is not unlike the shop pace where I spent 24 years as a toolmaker and I can tell you that implementing an efficient and accurate C/R on a 32-cavity mold in eight hours leaves no time for wandering or fantasy football discussions.
It is imperative the shop is well thought out from the hoist handl-ing system to the salvage tooling bins to keep maintenance moving and unencumbered by bottlenecks that can occur while technicians wait to move, bench, separate, clean, assemble and rack molds.
So we know our shop will employ at least four repair technicians, which means four benches minimum. Some of you might be wondering if four guys working on two benches can handle the same pull pace workload? Not efficiently. Ample bench space is imperative to a smooth flowing workload. Regardless of how well a shop is run there will always be the unplanned mishap, new mold arrival or scheduling addition that will require immediate bench space.
I have seen many shops that attempt to economize the shop budget and try to get along by having one or two benches shared by technicians working multiple shifts. This usually leads to confrontations concerning the upkeep of the bench and bench equipment, or someone being pushed to get their mold done. A craftsman's bench is just as important and personal as his tools and should be treated as such. The bench is where maintenance accountability really starts.
The workbench layout is the critical feature of a shop. The size, number, location and position of the workbenches relevant to the mold entrance and cleaning area will dictate the ease of mold traffic flow.
For this shop, four benches positioned in two parallel rows would be adequate since the shop is square versus rectangular. But with signs of future growth, we will plan for six benches for this shop, positioned in two rows of three. Since the shop will be engaged in many complete (daily) teardowns of multicavity molds, this will provide extra bench space to handle emergencies or to allow work on a chosen project mold that needs a total refurbishing.
Six benches will require the shop to be approximately 50'x 50', which will allow ample room for a cleaning area, storage cabinets, inspection bench and shop bench/desks for each technician. This also provides room for unencumbered personnel and mobile toolbox movement around the benches and easy monorail layout/installation overhead. A center aisle will be used to off-load molds right from the forklift to any bench.
When you make your living behind a bench, it is critical that the mold is at an ergonomically comfortable height, allowing you full control of plates and tooling during repairs. This is normally 34" for a person of average (5'-10") height working on molds no more than 48" tall.
Some benches are custom built with multiple levels, which allow you to disassemble a tall mold at the low end, say 20-25" then move the sub-components and assemblies to the fitting side, which stands 40" or higher. This puts you in position to better see, manipulate and fit small components.
Benches under 34" high will cause you to stoop—leading to back and shoulder troubles while a taller bench (over 36") will cause you to work holding your elbows too high and not leave you in good control of tall mold plates.
Bench length should never be less than 12 feet long unless you are maintaining very small molds of 1,500 pounds or less. Short benches won't allow complete disassembly of larger molds during the four stages of maintenance, which will promote incomplete repairs, mistakes and wasted time moving mold sections on and off the bench.
Bench Design and Construction
This is another area where costs get cut assuming just about anything will suffice as a workbench, as long as it will bear the weight.
A good example is steel saw-horse type benches where the plant fabricator welds a couple of six foot long, four-inch square rails to some legs. Sure it will hold a mold, but don't even think about trying to turn the mold/plates to a comfortable working position. It can easily slip off the rails and end up on the floor or your feet. Hand tools and mold tooling can't be conveniently placed on the bench during repairs as they too eventually end up on the floor, so you pile everything on your toolbox while you work.
Other Bench Points
- A bench top should be 3/8-inch thick steel with a one-inch radius on each of the four corners. You don't need a one-inch thick top to hold a 10,000-pound mold. The extra thickness of steel will easily add $1,000.00 or more to the cost of a bench. It is less expensive to add angle iron bracing under a 3/8-inch top every three feet across the width. This will add much strength and keep the top flat for years of service.
- You also should add a full-length, 1/4-inch steel shelf about a foot off the floor for storing all the gear it takes to maintain molds.
- Install at least four, standard 110v outlet boxes around the bench.
- Install at least four quick disconnect air couplings.
- Weld a ½-inch thick, 12"x12" plate to one of the legs on the corner of the bench for mounting (controller) 240v and 480v 3 phase outlet boxes.
- Install adjustable leveling pads under each leg (minimum of six legs for a 12-foot long bench).
- Mount a 5-inch machinist's vice on one end of the bench.
A commercially available bench with the features above is less than $3,000.00. As a bonus, some companies will even Blanchard grind the top after the bench is constructed for a dead flat surface. Smooth out the grinding marks with 180-grit paper on a disc sander, polish the top with wax and you are ready to go.