By Shannon Wetzel, Managing Editor
This story appears in the June 2017 issue of Modern Casting
When a part is designed to be put to market quickly, often the quickest or most familiar manufacturing method is chosen, like fabrication. But eventually, time and volumes might highlight deficiencies in the original manufacturing method of choice. This is a great opportunity for metalcasters, as companies start considering moving to a better optimized manufacturing process.
The casting process has many advantages, but it might require more tooling and engineering time up front than a weldment or machined component. Making those investments in tooling and engineering can pay dividends not just in reduced cost, but also improved performance, reduced weight, and even shorter lead-times.
One of the biggest hurdles for some designers is the unfamiliarity with metalcasting. As a metalcaster looking to convince a prospect to swtich to casting, where do you start?
Be a resource. Metalcasting facilities are well-versed in redesigning parts for casting. Share your examples, highlight the cost savings and other advantages and give them simple tips, like the ones in this article, to help pinpoint which parts in their inventory would be good candidates for casting conversion.
Signs a part needs a new method:
1. Insufficient dimensional stability
A casting’s dimensional tolerances are generally superior to welded and fabricated assemblies. A rotational and lift control post weldment for the oil market was experiencing distortion and stresses during fabrication that led to problems in assembly and in service. The cast version produced by Midwest Metal Products (Winona, Minnesota) eliminated the distortion and stress problems while also reducing cost by 38%. In cycle testing, the cast part demonstrated more than five times a longer life than the welded part.
2. Costly to manufacture and keep track of inventory
Pier Foundry (St. Paul, Minnesota), uses onsite visits to help customers identify candidates for castings. In one instance, the metalcaster and customer pinpointed a six-piece universal disc leveler pivot arm as a promising candidate. Using finite element analysis and casting process modeling, the engineers revised the part’s design to be optimized for casting. Converting the weldment to a casting freed up 71 minutes per unit of shop capacity and allowed the customer to focus its efforts on other products in their lineup. It greatly reduced the need for surge capacity in the spring. The part also saw a cost reduction of 60%.
3. Production volumes have grown, or a family of parts has grown so the number of parts and subcomponents has become unwieldy
Monarch Industries (Winnipeg, Manitoba, Canada) worked with a customer to redesign the mounting structure for tillage equipment. Each weldment contained an average of eight pieces of square and round tubing and plasma/laser cut plates. As the customer designed new pieces or new sizes and variations, the family of weldments grew to 17 different part numbers with a total of about 136 subcomponents. Each part number had to be kept in inventory for production and service requirements. Monarch worked with its customer to reduce the number of parts, optimize part strength and lower tooling and part costs. In the end, the customer converted its family of weldments into three castings used across equipment such as field cultivators, solid finishers, chisel plows and disc chisels. This provided an average reduction to cost of 30%, greater dimensional stability, improved aesthetics, and more plant capacity in the customer’s welding and fabrication departments.
4. Requires an excess of machining
Machining time is not inexpensive or particularly quick. Creating a design that reduces or eliminates the need for CNC machining frees up the equipment for other parts. In the case of an originally machined-from-billet steel part used in a piece of machinery, producing it in the investment casting process freed up valuable machine capacity for other critical applications. The conversion resulted in a 22% cost reduction. It also meant as-cast internal heat transfer capabilities could be added which were not possible when machining from solid. The casting supplier, Signicast Investment Castings (Hartford, Wisconsin) was able to incorporate a cooling internal passage with a turbine style directional cooling flow feature and rib features that enabled the part to be cast in steel rather than copper, which would have cost more with lower wear resistance.
5. The assembly is labor-intensive
A planter row unit for farm machinery was originally made as a 30-piece weldment that utilized fine thread nylock nuts for attachment. This made assembly time consuming and problematic. In addition, the stamped steel components had to be moved and stored multiple times throughout the production process. Dotson Iron Castings (Mankato, Minnesota) worked with its customer to redesign the row unit as a seven-casting assembly. This redesign included reducing 17 stamped steel parts of the main shank to three castings. The savings in assembly takt time ended up between 5 and 10%. Other benefits included improved seed placement accuracy and a more robust part.
6. Too much variation occurring from assembly to assembly
“In many cases there are quality issues with assembled parts by the time it is all welded together,” said Mark Hildebrand, director of sales, Monarch Industries. “The heat makes the metal warped and twisted. With casting, the holes and features will always line up.”
7. The market is ready for an improvement.
A dental furniture manufacturer identified a need for a high-end arm for reclining dental chairs and conducted surveys to find out what its customers wanted. The primary desires included an attractive part that was lightweight yet strong, ergonomic and cost effective, could hide tubes and wires, and provide a wide range of motion. To achieve these goals, the company departed from the typical bent tube/weldment combo and worked with L A Aluminum (Hayden, Idaho) on a cast aluminum version. The redesigned articulating arm assembly of aluminum castings has a hollow body for electrical wires and pivot points at each end to adjust the height.
Click here to read the rest of this story as it appears in the June 2017 issue of Modern Casting.