Application of Quality Control Method in Packaging Bag Production 2

Number of components per m AD 1 D 2
4 0.73 2.28
5 0.58 2.11
6 0.48 2.00
7 0.42 1.92 0.08
8 0.37 1.86 0.14
9 0.34 1.82 0.18
10 0.31 1.78 0.22
An example is given to illustrate the use of the mean and range controls. The production bag barrel with a bag length of 800mm requires a tolerance range of ±5mm. The unit automatically measures the bag length and prints, the value is accurate to 1mm, the number of detected pieces is 100, and the production order is divided into 25 groups, and the number of each component is 4. The above calculation method obtains mean and range control chart data.
X 0=800.44
UCLX=803.62
LCLX=797.26
R 0=4.36
UCLR=9.95
Based on the group number as the abscissa, the mean value and the range difference control chart can be drawn for each group's average value, each group's range is the ordinate, and the standard deviation σ=2.086mm, the standard bag length XO=800mm, and the actual bag length are calculated. The mean X-average value is 800.44mm, and the process capability index CPK=0.74 is obtained, which belongs to three levels, indicating that the process capability is insufficient, and a small number of defective products may appear. The root cause of the search error is mainly due to the fact that the traction tension of the bag-cutting machine is too large, resulting in slippage after being pulled tight, and the traction speed is not uniform. After adjusting the pulling tension, the pulling speed was uniform. A bag of 100 bags was collected again to measure the bag length. The plot data X 0 = 800.36, R 0 = 2.84, U-CLX = 802.43, LCLX = 798.31 were calculated in the same manner as above. UCLR = 6.48, also with the group number as the abscissa, each group of average, each set of range for the ordinate to draw the mean, range control chart.
All points did not exceed the control limits, indicating that the process of this process is stable. Divide the data into 6 groups, and make the frequency distribution table and histogram and calculate the standard deviation of the normal distribution curve and the dispersion range σ=1.38. Calculate the process capability index CPK = 1.12, indicating that the process capability is acceptable, but it must be strictly controlled and carefully tested, otherwise unqualified products will be easily produced.
When using the average control chart and the range control chart, it should be noted that the point on the control chart first does not exceed the control limit. In order to avoid erroneous judgment due to small amount of data, it is stipulated that there should be at least 25 consecutive points within the control limit to discriminate; secondly, we must pay special attention to whether there is an abnormality in the distribution pattern of the point, and its anomaly is mainly manifested in:
(1) There are more than 7 points in a row on the side of the centerline;
(2) There are more points intermittently appearing on the side of the centerline;
(3) Continuously rise or fall over 7 points;
(4) There is a clear periodic interval between the rise or fall of the point;
(5) More points are close to upper and lower control limits.
If the above situation occurs, the cause should be promptly identified and the necessary measures taken.
The above method of controlling the length of the bag barrel has been successfully applied in the production process of the unit. Firstly, the bag length data is automatically measured by the detection device, and then the data is processed by the microcomputer. The standard deviation, average value, range, and process capability index values ​​can be calculated, and the histogram, mean value control chart and range control chart can be drawn. , It can also complete the alarm function of control maps and distribution defects. (Finish)