needed to be ground in our system from about 90% to 30%. Tis reduced the finishing room size and allowed us to produce a better looking casting.” Marlatt suggested that if the gating
system can be designed to break off cleanly, you can eliminate or limit gate grinding entirely.
Te design of the core print in
your casting tooling also can have a significant effect on grinding, accord- ing to Fox. Te size of the prints and precision with which the core fits into the mold dictate the amount of core fin that must be ground away. “When you get the job in and
sample it, you have to see how much core fin you have,” Fox said. “If you have excessive core fin, [you must] tighten up the cores.”
3. Maintain Your Tooling Once you have properly designed
tooling, it’s important to keep it up-to- date with preventive maintenance. “Te quality of the tooling and the
upgrade maintenance [is critical],” Shah said. “If the tooling gets worn out and doesn’t have proper draft, you will end up with more grinding to do.” Prucha said tooling is important for eliminating core fin grinding. “Tink of defects that aren’t consid-
ered defects because they don’t result in scrap,” he said. “Core print filling is one example. If you have excess [room between the core and print], your core print can fill up with molten metal. On the flip side, if the print is too tight, you can generate sand in the mold.” However, according to Fox, tooling
concerns can be a long time coming for small to mid-sized job shops. “It’s more of an issue of getting [tooling] right the first time,” he said. “Once you get the fit with the core print on the tooling, it is not going to wear out over any immediate time- frame. On our aluminum matchplates, we check after 50,000 molds, which is a lifetime in our shop. We are just now seeing problems in tools from 1975.”
4. Install Tight Process Controls According to standard costing
models, molding is a relatively small portion of total casting cost. However, it can have a large effect on how much
40 | MODERN CASTING January 2012
is spent in the finishing room. Accord- ing to Roberts, the finishing time he and his colleagues were able to elimi- nate was made possible only through proper upstream casting processes. “We had a process that was in
control,” he said. “What I am talking about is the sand system if you are a green sand foundry. We controlled the sand to make sure we eliminated the problems of swell from sand molds that had poor mold wall hardness. If you are a metal mold foundry, you need to control the process mold temperature and metal temperature to eliminate the variations.” According to Paul Barker Jr.,
primary consultant for Barker and Associates, Fort Wayne, Ind., recurring defects in the casting process must be fixed in order to streamline the finish- ing room. Even a low level of scrap can build up, he said. Shah agreed. “Better process control of tem-
perature, mold hardness and binder percentage, all that is important,” he said. “Otherwise, it will cause gas and pinholes, metal penetration and cold shuts. [If you improve] process control, you will see reduced finishing times.” Fox said his company has made
an effort to ensure his molders on the floor are onboard with this idea. “You have to educate your molders
that any tear-up in the mold cav- ity can be costly,” he said. “Tey may think, ‘we can just grind that off,’ but we don’t want that. It is cheaper to plug the mold and remake it than to grind it off. We tell them, if you have a 10-on pattern and you have a tear-up, that is 10% scrap. When you have a plant going for 4% scrap, that’s a lot.” For job shops, it can be more critical
to hone the upstream metalcasting pro- cesses than in high production shops. Where continuous flow finishing can make up for lost time when the same casting comes through grinding again
and again, a more precise casting often is required to shave time in a job shop. “If you have a 0.5-in. wall or a
surface that is 2 in. high, can you take 0.06 in. off that surface?” Barker asked. “If you can reduce any amount of metal, do it. Saving metal not only saves you money on the raw materials, but it also eliminates finishing time.”
5. Steal From Other Departments When all else fails: steal resources
from other areas of your plant. Prucha points to one Midwestern casting facility that fixed its finishing room bottleneck by cross-training molding personnel. When castings were wait- ing to be ground, the company started sending its molders to the finishing room to help it catch up. Molding can be manipulated in
other ways to assist finishing, accord- ing to lean manufacturing consul- tants. In a job shop environment, part scheduling on the molding line can be done with an eye for ease in grinding. For example, a facility can ensure no more than two different parts are sent through to the finishing department at one time, resulting in limited change- overs and better continuous flow. Te inspection department also
can help. In the early 2000s, Conbraco Industries Inc., Conway, S.C., found a way to limit the number of cast- ings it needed to grind by performing real-time x-ray on all new jobs and current jobs undergoing a process change. If the x-ray detected problems with a casting, it never made it into the finishing room’s queue.
Many finishing operations can be eliminated by fixing upstream process errors, like excessive core fin.
ONLINE RESOURCE
Visit
www.moderncasting.com for an additional article on finishing room fixes.
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