Talking about IQC (III): How to gradually cancel IQC?

Earlier, we discussed the necessity of incoming inspection and how to choose the way of incoming inspection from the economic point of view. We also mentioned the location of acceptance sampling. At the same time, I also mentioned that the ultimate goal of incoming inspection is to gradually reduce or even cancel incoming inspection. The reality is that incoming inspection is not less and less, but more and more. This is mainly due to the self-protection and insecurity of the management responsible for the operation. Just like when implementing lean production, reducing inventory or eliminating the psychological pressure caused by inventory to management is the same. As a general manager said, if there is no stock in the warehouse, you can't sleep well. Although reducing or canceling the incoming inspection may bring some difficulties to the operation in a short time, it is also the price that any change needs to pay. But in the long run, the cost savings for the company are very considerable. Today, we will discuss how to reduce and cancel the incoming inspection according to our own experience. If the incoming inspection is to be cancelled, it must be controlled from the source, which is the supplier's ability, mainly referring to the process ability and quality control ability, both of which are indispensable. In other words, when the supplier's process capability is good enough and the supplier's process must be stable for a long time, the incoming inspection can be cancelled. Here, I will introduce it in two situations. 1 The situation is about how to realize the non-receipt inspection of brand-new products; The second situation is how to gradually reduce the operation of canceling the incoming inspection of mass-produced products.

Let's look at the case of 1 first, how to cancel the incoming inspection of new products. Next, I will systematically introduce the main points of each stage according to the ideas of supplier development and management.

In the first step, when selecting suppliers, we must avoid price-only theory. We should evaluate them through "total cost of ownership", that is, in addition to the initial price, we should also consider quality-related costs: incoming inspection, material review, output loss, downtime, extra inventory, etc. We must evaluate the technical ability and quality control ability of suppliers at the same time, that is, the supplier system audit and technical review must meet the requirements, otherwise, there will be endless troubles. If the supplier cannot meet these two requirements, it will be very difficult to cancel the incoming inspection in the future.

Second, in the supplier's process development stage, our SQE must participate in the supplier's process development and control design to ensure that the process has sufficient capacity and control. For quantitative product characteristics, the production process must have high enough capacity, at least CP; 1.33。 When I introduced the difference between process capability and process performance, I said that if the process capability is inherently insufficient, even if the quality control capability is good, there will be a certain number or even many defective products flowing to our factory. In this case, incoming inspection is very important. According to Deming kp rules, 100% inspection is required. Quality control ability mainly refers to the ability to keep the production process stable and controlled. If the process capability is good, but the process is often out of control, then a certain number of unqualified products will definitely flow to our factory. In this case, it may be necessary to conduct acceptance sampling. In addition, for product features that cannot be quantified, such as missing and wrong assembly, error-proof devices must be used in the process.

The third step is to verify the supplier's process capability and process stability. Before mass production, we must conduct a strict process audit of suppliers. The purpose of audit is not only to review the compliance with the control plan, but also to pay more attention to the adequacy of process control and determine the opportunity for improvement (OFI). In this process, you must personally go to the supplier's site to witness the whole production process, and make statistics on process control conditions such as qualified rate, process capability/performance (Cp/Pp) and control chart performance. This step is very critical. Our SQE often has no time or is unwilling to go to the supplier's site to do these things, just looking at the report submitted by the supplier. This is not right. We spend more time at this stage, and we can completely cancel the non-value-added operation of incoming inspection after mass production.

Fourthly, in the initial stage of mass production, we need to monitor the quality performance of suppliers for a period of time. The easiest way is for our SQE or QE to accept the products to be shipped before the supplier delivers them. According to experience, 4-5 batches are enough, mainly depending on the qualification rate, Cpk and data point performance on the control chart. If the process performance is stable, the failure rate is very low, and Cp/Pp is greater than 1.33, it means that the supplier's process is controlled and the process capability is acceptable. In this case, the incoming inspection can be exempted. If the process shows instability, the supplier must conduct a 100% full inspection of the products before shipment, and at the same time study the causes of process instability and take corrective measures. And it is necessary to carry out 100% full inspection on suppliers until the process performance is stable and the unqualified rate is extremely low. At the same time, collect the defects of our own production line and customers in detail. Personally, I don't recommend 100% inspection of suppliers' parts in our factory, because we may not have the necessary testing means, venue and testing environment.

Step 5: After mass production, the supplier is required to provide the size report, control chart and Cpk/Ppk data of each batch of products, so there is no need for incoming inspection. Continuously receive the performance of suppliers' products in our production line and customers, and give feedback to suppliers regularly.

In this process, the stability and controllability of the process and the low failure rate are the two most important factors, especially the former. If the process is unstable, the incoming inspection with acceptable sampling inspection will be carried out all the time; If the process is stable, but the unqualified rate is greater than the break-even point Pb, 100% incoming inspection is required. If the process is stable and the failure rate is less than the break-even point Pb, although the incoming inspection can be cancelled, the failure quality cost is unacceptable. According to my experience, under normal circumstances, the break-even point Pb is very low, because we usually consider the worst case where after-sales claims flow to the end customers and affect the customer's quality rating. Because the labor cost in China is low, the inspection cost is not very high. For example, if we check the appearance and size of the painted bumper (assuming that the paint is not damaged), the cost will be 5 yuan, but if we claim after sale, it may be 2000 yuan, so Pb=0.25%. In fact, this ratio is challenging for the bumper industry. According to Deming kp rules, only 100% of the goods can actually be inspected. However, this 100% inspection is generally not completed in our factory, because we don't have the site, lighting and personnel needed for inspection, and it is easy to cause secondary damage to the products, so we must carry out 100% delivery inspection before packaging at the supplier to replace our incoming inspection. If the damage caused during transportation is ignored, in fact, delivery inspection and incoming inspection are equivalent. Our understanding of incoming inspection should not be limited to the place of inspection, but whether the purpose and method of inspection are the same. We generally don't use the supplier's delivery inspection instead of our incoming inspection because we don't trust it.

Let's discuss the second situation, how to gradually reduce the incoming inspection of mass-produced products. This situation is actually a breakthrough to the status quo and can be completed as a six sigma DMAIC project.

The first step, because it has been mass-produced for a long time, we should have enough historical quality data, including incoming inspection, production line and customer performance. According to these historical quality data, we classify these products, and the 1 category is a product with good overall quality performance for a long time, far below the breakeven point Pb; The second category is products with poor quality performance, which is much higher than the break-even point Pb; Category 3, products with unstable quality performance, that is, products that fluctuate around Pb.

The second step is to conduct a comprehensive and detailed process audit of the production process of these products, not only to confirm compliance, but more importantly, to confirm the adequacy of control F. It is recommended that experienced SQE complete this process audit, and VDA6.3 is recommended in the audit form, and the risk rating of process control is low risk and high risk.

The third step, combined with the classification of the first step and the results of the process audit of the second step, determines the way of product incoming inspection, and suggests following the following principles:

1 product+low-risk process control: inspection-free.

Category 1 product+high-risk process control: inspection exemption+corrective measures to stabilize the process. This may happen when the process capability is very strong. Although unstable, the worst batch is also lower than Pb.

Category 2 products+low-risk process control: 100% inspection+redesign supplier process to improve process capability.

Category 2 products+high-risk process control: 65438+ 000% inspection at the supplier+immediate corrective measures in the control process.

Category 3 products+high-risk process control: acceptance sampling)+immediate measures to stabilize the process.

The fourth step is to repeat the first step to the third step regularly (every month), so as to gradually reduce the purchase quantity of products.

Finally, I emphasize that the product inspection here is aimed at specific product characteristics, that is to say, the same product parameter A may be exempted from inspection, but parameter B needs 100% full inspection. For example, the bumper mentioned above may be exempted from inspection, but its appearance and color may need 100% inspection. In this way, we can optimize the cost of incoming inspection from three aspects, namely, reducing the number of product features, reducing the number of samples and reducing the frequency of inspection. Let's call it a day.

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