Value$-$Stream Mapping Data Set

TWI Industries

TWI Industries produces several components for tractors. This case concerns one product family$-$Steering Arms$-$which are produced in many configurations. TWI's customers for this product family are both original$-$equipment tractor builders and the aftermarket repair business.

Because of the wide variety of product configurations and the fact that customer configuration requirements vary from order to order, steering arms are a "make$-$to$-$order" business. It currently takes a customer order $27$ days to get through TWI's production processes. This long lead time and a significant order backlog have prompted TWI to quote a $60-$day lead time to customers. However, TWI's customers cannot accurately predict their size requirements more than $2$ weeks out, and thus they make adjustments to their orders $2$ weeks before shipment. These order adjustments lead to order expediting on the shop floor at 'TWI.

Although TWI Production Control releases customer orders to production roughly in the order that they are received, orders are batched by product configuration on the shop floor to reduce the number of time$-$consuming changeovers. This also creates a need for order expediting.

The Product

A steering arm is a metal rod with a forged fitting welded to each end.

TWI's steering arms are available in $20$ different lengths, $2$ diameters, and with $3$ different types of end fittings. $($Each end of the steering arm can have a different fitting.$)$ This means there are $240$ different steering arm part numbers that 'TWI supplies.

Customer Requirements

$24,000$ pieces per month.

A customer order ranges from $25$ to $200$ pieces, with an average of $50$ pieces.

Corrugated$-$box packaging with up to $5$ steering arms in a box.

Several daily shipments per day by truck to various customers.

Each customer's configuration requirements vary greatly from order to order.

TWI requires orders to arrive $60$ days before shipping date.

Customers often adjust their size mix $2$ weeks before the shipping date.

Production Processes $($see diagram$)$

TWI's processes for the steering arm product family involve cutting a metal rod followed by welding end fittings to the rod, deflash $($machine removal of excess weldment$),$ painting at an outside vendor, and subsequent assembly of the end fittings. The forged end$-$fitting sockets are also machined at TIVI. Finished steering arms are staged and shipped to customers on a daily basis.

Switching between rod lengths requires a $15$ minute changeover at the cutting, welding, and deflash operations.

Switching between rod diameters takes a $1$ hour changeover at the cutting, welding, and deflash operations. 'The longer changeover for diameters is due mostly to an increased quality$-$control inspection requirement.

Switching between the three types of forged end fittings takes a $2$ hour changeover at the machining operation.

Steel rods are supplied by Michigan Steel Co$.$ The lead time for obtaining rods is $16$ weeks. There are two shipments per month.

Raw forgings for the end fittings are supplied by Indiana Castings. The lead time for obtaining forgings is $12$ wecks. There are two shipments per month.

Work Time

$20$ days in a month.

Two shift operation in all production departments.

Eight $(8)$ hours every shift, with overtime if necessary.

Two $15-$minute breaks during each shift.

Manual processes stop during breaks.

Unpaid lunch.

TVI Production Control Department

Receives customer orders $60$ days out and and enters them to MRP$.$

Generates one "shop order" per customer, which follows the order through the entire production process.

Releases shop orders to production $6$ weeks before shipment to accelerate MRP$\text{'}$s procurement of rods and forgings.

Issues daily "priority" list to production supervisors. Supervisors sequence shop orders through their departments according to this list.

Receives customer size$-$changes $2$ weeks before shipment and advises supervisors to expedite these orders.

Issues daily shipping schedule to Shipping Department.

Process Information

Cutting $($The saw cuts rods for many TWI products$)$

Manual process with $1$ operator.

Cycle Time: $15$ seconds.

Changeover time: $15$ minutes $($for length$)$ and $1$ hour $($for diameter$).$

Reliability: $100\%.$

Observed Inventory:

$20$ days of uncut rods before the saw.

$5$ days of cut rod.

Welding Workstation I $($dedicated to this product family$)$

This operation welds the first machined forging to the rod.

Automatic process, with operator load & unload external to machine cycle.

Cycle Time: Operator $=10$ seconds, Machine $=30$ seconds.

Changeover time: $15$ minutes $($for length$)$ and $1$ hour $($for diameter$).$

Reliability: $90\%.$

Observed Inventory: $3$ days of welded arms.

Welding Workstation II $($dedicated to this product family$)$

This operation welds the second machined forging to the rod.

Automatic process, with operator load & unload external to machine cycle.

Cycle Time: Oper