A manufacturer of engineered hinges, custom stampings, and assemblies for the automotive industry fears the loss of current and future business because of late shipments and defective parts. The customer has found several defective hinges in the shipments, some missing a spot-weld and some that are missing a part completely. Electronic error-proofing devices and 100% inspection have not prevented these defects. The cost of the internal and external sorting is more than the business can absorb. The customer demand is growing, and they are tired of a supplier that cannot deliver a defect-free product on time.
Day one on the shop floor:
Several operators were picking the parts from a shipping tote, unwrapping them, and placing them onto a tabletop. The parts were greased in batches of ten and then hand-carried to another work surface next to the pin insertion machine. One operator would assemble the parts in the machine and then place them into a partitioned box and carry the box to a skid. The partially assembled products passed from one operator to another. The pin insertion machine waited between batches of parts. Three workers had been hired from a temporary services business a few days earlier, and the fourth person instructing the others had been doing these assemblies for several weeks.
The assembly for this product was in a small room of the building confined by four walls and an entry ramp. and shared the space with assembly benches and materials for several more products. Supplies were placed wherever there was an open space. Moving components and finished goods was difficult because of the congestion. The fixture for this product was programmed to sequence the tasks using sensors to detect the parts. Completed boxes of parts were 100% visually inspected for defects before shipment. A service at the customer’s location was hired to re-inspect the products 100% as required by the customer.
The manufacturer spot-welds two different sub-assemblies for this hinge. The stampings for these sub-assemblies snap together before being clamped into the fixture that holds the parts at a precise orientation. The operator cycles the spot welder for one spot-weld on one side of the part and then, with significant physical force, throws a heavy lever, pushing the fixture to the other side to do the second spot-weld. He works with thick cotton gloves to remove the finished piece because of the intense heat permeating the piece after the welds. After making several hundred of these “Part A’s” – over several shifts - the weighty $10,000 fixture is removed and, after a few hours’ labor, a different $10,000 fixture is put in its place. The spot welding of several hundred “Part B’s” begins. Two spot-welds are also done on Part B, but Part B is not identical to A, nor are the welds in the same places in space. In both cases, the operator throws a heavy lever to move from the first weld target to the second. The pieces are checked in a gage, then put into containers for shipment to paint.
The Findings
The training of the operators was inconsistent. Each operator needed to create his/her method. The room was uncomfortably hot in the summer and cold in the winter. Clutter was everywhere, requiring moving several pallets to get to the one needed. The operators found it easier to carry small bundles of parts to the worktables and were tempted to use parts nearby from containers that the defective tag may have fallen off. The operators were working bent over tables. Workers were often replaced for not showing up to work, and temporary workers rarely achieved the 90-day probationary period. The work instructions explained how the parts go together. The operators often traded tasks during each shift.
The assembly area was comprised of a hodgepodge group of leftover worktables and shelves. The lighting was too dim for employees to easily see paint defects or missing grease. The parts identified with “defective” labels remained inside the assembly room and added to the overall clutter which slowed operators.
Spot welding was riddled with needless complexity, was bleeding money in the form of labor/time/ electricity/ defective product, and a premier international customer was about to pull its business. The complexity began with the assumption that a fixture salesman was correct when he sold the two fixtures. He claimed two spot welds could not be done in one stroke, and he claimed Parts A and B could not be done in one fixture. There began a litany of labor-intensive and error-inducing procedures: no check during the process to ensure that both spot-welds were made; the completed spot-welds were difficult to see in later checking; and the fact the pieces snapped together misled checkers into thinking the pieces were fully welded. The part counter on the machine counted the machine strokes instead of the number of parts completed, sometimes causing the operators to record twice as many parts into inventory as they had produced. Loading and clamping each piece into the fixture took time. Throwing the heavy lever between spot welds physically exhausted the operators, wasted time, and jarred the fixture repeatedly which then required constant adjustments and repeated set-ups from maintenance. The welds were over partially hollow metal, requiring the welder to arc the gap and use extra amperage. The extra heat generated throughout the piece creates a potential safety issue and thermal distortion of the final dimensions. This machine was also the bottleneck of all the operations for this final assembly.
A. Stout’s Solutions:
One dedicated operator for each product, instead of two, now makes complete assemblies one at a time in a defined sequence. Posted instructions consist of a physically labeled model of the parts in order of assembly. Additional warnings to achieve quality assemblies are affixed to the physical model and the assembly fixtures. All non-essential items have been removed from the area and task lighting added. Locations dedicated to each part are defined and labeled next to the operator. Through iterative problem-solving questions and feedback, the operator discovers deeper insight into his or her work. The quality manager goes through each box with the operator. The operator is challenged to achieve certification by demonstrating zero defects in this assembly for three consecutive weeks; the certified operator is audited but no longer requires 100% inspection. The transition to improve these two manufacturing areas was completed within 2 weeks.
A spotweld fixture was designed by the company’s quality engineer and manufacturing engineer instructed by Art Stout and built in-house that does both spot welds simultaneously and does both Part A and Part B without changeover. Further, the pieces are held in location with pins and magnets; there is no need to clamp and unclamp. There is no lever to throw, so jarring and exhausting operator movement is eliminated as well as downtime due to maintenance reset. The arrangement of materials is organized nearer to the spot welder, eliminating unnecessary operator movement during the process. Corrections to the flow of coolant are made to keep the part cooler and thus reduce the shrinkage caused by the heat. This minimizes the movement of the part during welding and eliminates the need for constant adjustments. As the fixture is being tested, exact measurements of the initial test sub-assemblies measured on a coordinate measuring machine are used to adjust the fixture, not inexact go/no-go gage information. The cost of material for the new fixture was $2,000 including two Teeter-Tip (double welding) devices, like the ones found in the storage on site.
The Results
Dan, the operator responded positively to the improvements to organize his workspace and make his job easier. When defective parts were found, Dan initially commented that he does not make bad parts and that someone sabotaged his work. Subsequently, the inspector and Dan inspected the parts together, and the team helped Dan improve his output from 20 pieces/hour to 60 pieces/hour. When challenged to see if he could touch each part only once, Dan himself further increased his output to 80 pieces/hour. Joe the spot weld operator increased his output from 60 pieces per hour to 210 pieces per hour.
Company leadership saw what could be accomplished, that defect-free products could be made at rates faster than anticipated. They learned they had to invest time in their employees. They picked the one project with the greatest ROI and fastest payback. They learned that root problems must be fixed first and many nuisance problems subsequently disappear. The mindset of the leadership changed, specifically the belief in the possible. The payback time was less than the length of this 3-month improvement project.
The earnings for the original 75,000 pieces became positive because the hourly output increased from 20 pieces/hour to 60 pieces/hour with the existing assets. The average earnings in NAICS sector 33 are 7.4% of sales. This company’s earnings grew $172,500 because of the additional production of 37,500 $10 parts. The only additional cost for these parts is the material cost at 54% of sales in NAICS sector 33.