Assembly in Action: The Old Grind Is Not What It Used to Be
This manufacturer of food waste disposals and hot water dispensers needed to increase production of the steel motor shell that houses the electric motor and stator. These food waste disposals range from 1/3 to 1 hp for residential units and 1/2 to 10 hp for food service units in commercial applications.
The company used to take a stamped steel sheet and roll form it to the correct diameter. Next, they would MIG-weld or resistance-weld the seam, expand it to the correct diameter and then put it in a lathe to cut and chamfer each end. This process would help ensure burr-free ends and keep the ends parallel. This procedure required handling between each station and a significant cycle time for each finished motor shell. It was also too slow to keep up with demand.
Newcor Bay City Div. (Bay City, MI) provided a better way to perform this procedure. Through automation, a motor shell starts with a mild cold-rolled steel blank that ranges in thickness from 0.047 to 0.049 inch. After a steel strip is blanked on a press, the blanks are palletized and placed in moveable stacks. They are then placed on the motor shell machines' conveyor and fed into a destacker. Here, an arm using suction cups picks up each blank. The steel blank is then roll-formed and transferred down the index rail to a mandrel where it is clamped. The edges are aligned within ±0.002 inch. The edge alignment is critical because it aligns the motor stator and the rotor. If it's off, the rotor shaft will not align properly, causing other manufacturing problems.
After clamping and alignment, the shell is resistance-welded using a mash seam weld. Then, it is sent to the process line part of the machine where the imperfections on the weld are nipped off. This process is used to keep both ends of the motor shell parallel. At the next station, two witness marks are stamped into the shell to align all the end parts to the motor shell. The motor shell is placed on an expander that increases the diameter about 0.03 inch.
The expander is important. During roll-forming and welding, the motor shell tends to taper. Expanding the steel beyond its yield point allows it to hold the diameter and not be subject to temperature changes.
With the motor shell equipment, the company was able to decrease cycle times, reduce scrap and get a better shell. The company now has three motor shell welders that run 24 hours a day, at least 5 days a week. They also run 5 to 8 hours on Saturday, as needed. Cycle time is 6-seconds per motor shell. Each machine also has the capability to easily be changed over to a different motor shell. The shells have the same diameter but different lengths.
On the latest motor shell welder, a servomotor is used to control the welding speed instead of an air-over-oil cylinder system. Now, pressing a button controls weld speed for different lengths of motor shells rather than setting switches. Currently, one employee services three machines.
For more information on automated welding, call Newcor Bay City Div. at 517-893-9505, visit www.baycity.newcor.com.