Application of Quality Control Method in Packaging Bag Production 1

In this paper, the principle of mathematical statistics is used to explain the error distribution rule of the length of the packaging bag produced by the ZXJ-1000C automatic printing and bag making unit, and the use of histogram, process capability index, average-range control chart to control the production process, and ensure packaging Bag bag length quality method.
Bags occupy a very important position in the packaging products, such as cement, flour, starch, feed, fertilizers, chemical raw materials, agricultural and sideline products and mineral products such as powder and granular materials are mostly bag packaging. The length of the bag determines the volume of the bag, and ultimately determines the amount of goods. The length of the packaging bag is insufficient, which can easily lead to breaking of the package or insufficient amount of goods during potting and damage the interests of the customer. The length of the packaging bag is too long, resulting in waste of packaging materials and detrimental to the interests of the production enterprise. To increase the accuracy of the package quantification, we must first control the length of the package.
ZXJ-1000C Automatic Printing Bag Making Machine (hereinafter referred to as the unit) is a professional equipment for producing packaging bags. It is equipped with an online measuring device that can automatically measure the length of the bag during the production process and print the sampling data. According to the above, the stability of the production process can be determined by using the X-average control chart and the R-range control chart, and the unstable factors in the production process can be found and eliminated in time to ensure the accuracy of the bag barrel length.
Bag barrel length error and distribution pattern The unit adopts changing the gear ratio between the cutter and the traction to achieve different bag length adjustments. When the cutting speed is fixed and the pulling speed is slow, the cut bag is short. When the pulling speed is fast, the cut bag is long. Once the transmission ratio is fixed, the length of the cut bag is fixed. It is equal to the length of the reciprocating bag barrel, which is the nominal bag length. However, testing the length of a batch of bags will reveal that, except for a portion that is just equal to the length of the nominal bag, some are shorter than the nominal length of the bag, and some are longer than the nominal length of the bag, and the number of excesses and shortfalls is approximately equal. According to the principle of mathematical statistics, this phenomenon is normal. For example, the nominal bag length of a production cement packaging bag is 800mm, and 100 inspections are randomly selected in a batch of bag cylinders. The maximum length is 805mm, and the shortest is 796mm. The distribution range is 805-796=9mm.
Take each length of bag tube as a group, a total of K groups, calculate the frequency of each group. If the length of each group of bags is the abscissa and the frequency is the ordinate, the frequency distribution histogram can be drawn. The top edge of each column of the histogram is connected with a smooth curve. This curve reflects the frequency distribution rule of bag barrel length, which is the actual distribution curve. If there are many pieces detected and the group distance is very small, the smooth curve can be described by the theoretical curve—normal distribution curve. According to the normal distribution theory, an important parameter standard deviation σ in the normal distribution curve can be calculated.
The allowable error of the length of a given bag is generally given in the production. The error of the length of the produced bag should be within this range. This depends on the quality of work of the production process, ie, the cut used in the bag cutting process of the unit. Bag machine performance is closely related. The degree of assurance of the production process to the work quality is called the process capability. The common process capability index, CPK, is used to represent the formula: CPK=(T-2XO+2X mean)6σ. Where T is the allowable tolerance range for the bag length, XO is the standard bag length value, and X mean is the average value of the actual bag length. Process capability is divided into five grades: special grade, grade one, grade two, grade three, and grade four. If the grade is too high, the process capability is too full and not economical; if it is too low, the process capability is insufficient, and unqualified products will appear. If the process capability index CPK belongs to the second level, indicating that the process capability is acceptable, monitoring should be closely watched.
The quality control method of the bag barrel production process To verify the stability of the bag cutting process and understand the dynamic situation of the quality parameter change over time, the quality control of the production process can be performed by using the mean control chart and the extreme difference control chart in combination. The specific method is to divide the bag length data detected by the unit into K groups in the order of m. Find the average X-average value of each group and the range R of each group. Draw the mean and range control charts respectively. . The average control chart mainly observes and analyzes the changing trend of the average value; the extreme difference control chart mainly observes and analyzes the dispersion of accidental errors. Determine whether the process is stable based on the points on the control chart, the center line, and the upper and lower control limits.
The center line of the mean chart: X 0 = the number of sets of mean values ​​for each group. The center line of the control chart: R 0 = the upper line of each group and the average value of the control chart: UCLX=X 0+A ·R 0
The lower control line of the mean chart: LUCX=X 0-A·R 0
Upper Control Line of Range Control Chart: UCLR=D 1·R 0
The lower control line of the range control chart: LCLR=D 2·R 0
Among them, the values ​​of A 1, D 1, and D 2 can be determined from the control chart by the coefficient table (to be continued)