GM Sport Utility “Envoy” Sub Assembly Dial Table

The dial table is a large fixture that rotates through a sequence of automated stations that apply additional components. This system is initiated by an operator at the beginning of each cycle. The operator places the required parts (two base components at one time) on the pallet and then initiates the indexing of the dial table for the next pallet to advance. While the operator is placing parts on the next pallet the automatic operations finish the sub – assembly and exit finished sub-assemblies from the machine. The finished sub assembly is called a pivot housing.

Basic Steps in Operations

  1. Raw material on conveyer presented to operator
  2. Operator places parts on pallet on dial table. (Some assembly done)
  3. When operator is finished placing parts on pallet, operator initiates dial table to index.
  4. Dial table automatically finishes previous parts while operator is placing parts.
  5. When part indexes around to offload shoot it is exited out of the machine into a WIP area.
  6. WIP is stored / ready for transport.

Process Flow

  1. Raw material in storage.
  2. Parts places of pallet/some assembly done.
  3. Dial table finishes assembly on previous part.
  4. Finished product transported off dial.
  5. WIP
halden-zimmermann-process-flow

Process Flow 

Time Analysis

Notes:

  • Since this is a dial table parts exit at through put time or cycle time.
  • Fixtures in the dial table are fixed. Dial table can only have maximum of 24 parts in system unless operator misses cycle. (Table always full during test)
  • Each cycle two parts are placed, and two parts exit system at the same time/ pallet holds two parts. (two parts placed and exited, estimated stocked multiplied by 2)
  • Twelve pallets in the system
halden-zimmermann-time-analysis

Time Analysis

 

Average Throughput:22.7 seconds / part

Average Lead Time:270 seconds  

Actual Stock:24 parts 

Estimated Stock:11.89 *2 =23.7 parts in stock (Little’s Law)

 -Or –

Average Throughput:2.643 parts /min

Average Lead-time:4.5 minutes

Estimated Stock:11.89 *2= 23.7 parts in stock (Little’s Law)    

(Ave Stock= Ave throughput* Average Lead-time)

Little’s Law

Little’s Law works for the dial table operation. The actual number of parts that are in stock is 1.25% off from the estimated number using Little’s Law. 

Actual # parts in System:24

Difference: Observed – Little’s Law:.3

Percent Error:1.25%

Differences between Estimated and Actual:

There is a small difference between the actual and the estimated stock using Little’s Law. This is because of the operator variability from part to part. There is a range of throughput times that is calculated over the 20 observations. 

Reducing Error:

More cycles measured would reduce the error.

Reduce operator variability for each cycle/ standardize/ raw pats presentation.

Measurement error with the timing process. (Hitting the start and stop on stop watch)

Raw Process Time Estimation:

For the raw processing time dial table index time was eliminated from the calculation. The time that is required to pick up parts from the raw material conveyers is eliminated. The time that the operator actual places parts on the fixture is the raw processing time.

Ave Raw Processing Time (Throughput):17.5 secs /part

Estimated Lead Time:210 secs

Dial Table Capacity: 

Using Raw Processing Time

Long Term Maximum Throughput:1645*2 = 3291 parts / 8 hours

    789840 parts / year (240 days 1sft)     1579680 parts / year (2 shifts)

Using Average Processing Time

Long Term Maximum Throughput:1269*2 = 2537 parts / 8 hours

    608880 parts / year (240 days 1sft)

    1217760 parts / year (2 shifts)

Bottle Neck Operation:

The bottle neck operation is the operator placing the parts on the fixture in the dial table. This can be understood in two ways:

Cycle time of the dial table is less than the operator

(Easy Way) All the other operations are done prior to the operator initiating the next cycle.