Ken PerimanProblem solving,Sub frame bolt issue

Problem Statement

Sub frame bolt loose and initial appearance was identified as a supplier issue

Initial investigationA vehicle was found on the test track with an underbody noise. This vehicle was evaluated at Chassis Repair as having a front lower control arm bolt loose. 1. SQ requested Supplier torque data: the data shows E-

16.55 16.6. L- 16.59, 16.55, 2. Clean point requested from supplier and provided as

Sequence #: 1179. 3. SQ also asked if Assembly could have reversed this at

Chassis 2 station 2 process and requested data on KMMG GA lift assisted tooling.

4. No info documented on the CVIR of any repairs or issues related to this issue.

InvestigationInitial investigation started a the review of the pictures on the turnover log. As noticed in the picture below the nut is not torqued down. If the part was torqued down then there should be threads showing above the top of nut. Also in the picture there is a blue paint mark on the nut, this is to identify that the torque process was complete. Also in the picture there is blue paint on the opposite side from the nut. This suggests that the part was torqued then loosened. Supplier data also confirms the lower arm bolt for this vehicle was properly torqued.

Supplier paint mark to verify torque process completed on nut.

Blue paint on the threads of the bolt. Opposite side from nut.

Data from supplier showing the suspect vehicle as properly torqued.

suspect vehicle

InvestigationAfter reviewing the pictures and data the next step was to review the process. At Chassis 2 station 2 there is a torque confirmation that is done with a large D/C tool driver. This driver is supported on a lift assist system for ease of use for the operator. While watching the process it was noticed that the driver will, when placed on a bolt to torque, attempt to turn the bolt and if the torque is high enough the driver will reverse about 1 turn then reverse again and tighten the bolt to proper torque. If the bolt is not at a high torque level then the drive will continue forward to the proper torque and stop.

These are the 4 locations at Chassis 2 that are torqued with the large driver Large torque

driver

InvestigationAt the front of the vehicle there are 2 bolts that are the same size (this was confirmed by Ken Periman by placing the driver on both bolts). These bolts are 1. for the chassis marriage and 2. the other is the issue bolt for the lower arm.

Side view of front right of vehicle

Chassis Marriage front bolt

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1

Lower arm attach bolt

2

Bottom view of front right of vehicle

Investigation ResultsIt appears, according to the previous data and data below, that the team member (leader) at the

station during shift change loosened the (#2) lower arm bolt instead of torquing the chassis marriage bolt. As stated before, the bolts are the same size, the driver will loosen a bolt that is of high enough torque and, because the lower arm bolt has a nut ,the driver did not tighten the bolt. Supplier data confirms that the part for this vehicle was properly torqued and they have confirmed that there was no rework performed. Also, (Below) the torque history shows the first bolt never made it to torque. The first bolt in their process is the same as shown below (1). Additionally the chassis 2 station 2 team member tracking log has missing information for the issue vehicle which was sequence # 649.

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No Sequence # 649

Conclusion & ContainmentSupplier provided a clean point. SQ worked with Assembly to provide information about this

issue and help determined a countermeasure for this issue. A suggestion recommended is that when there is a vehicle that has been identified as not having met the torque specifications then the keeper should confirm the torque of the chassis marriage (4) bolts as well as verify that the lower arm was not inadvertently loosened. As the torque requirement is 160N to 180N for the lower arm and the chassis marriage bolts in the front are also 160N to 180N then the keeper can check that the lower arm is properly torqued as well as the chassis marriage bolts.

This has improved failures significantly and has removed the assembly shop from issues of loosening the chassis bolts.