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注塑工艺参数优化

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培训课程 2

工艺参数的优化

受训者手册

德马格注塑机工艺参数优化的步骤指导

页面周期分析 3 注塑工艺参数优化 6 步骤 1: 找出转压点 7 步骤 1结果 8 步骤 2: 找出保压时间(浇口冷凝时间) 9 步骤 2 结果 10 步骤 3: 优化注射速度 11 步骤 3 结果 12 步骤 4: 采用正确的螺杆转速 13 步骤 4 结果 14 步骤 5: 优化多级螺杆转速和背压曲线 15 步骤 5 结果 16 步骤 6: 优化松退 17 步骤 6 结果 18 步骤 7: 优化保压曲线 19 步骤 7 结果 20 TABULATED RESULTS 21 步骤 8: 优化锁模力 22 步骤 8 结果 22 步骤 9: 设定注射压力 23 步骤 9 结果 23 典型工艺参数公差设定 24 2

成型周期分析

采用下面表格估计注塑过程中的每一阶段对周期的影响. 然后去机床看正在运行的模具, 写下实际的时间并计算出百分比.

哪一阶段在整个周期中占最多的时间?

那里可以是最有效的缩短成型周期

模具 1 估计 % 实际实评价际% 合模射台前进和后退注射时间保压时间冷却时间开模顶出整个成型周期 100% seconds 100% 4

模具 2 估计 % 实际实评价际% 合模射台前进和后退注射时间保压时间冷却时间开模顶出整个成型周期 100% seconds 100% 5

工艺参数优化

目标:

• 一步步改进工艺过程稳定性.

• 评估各个参数的更改对工艺过程稳定性的影响

• to demonstrate the cumulative improvemnt in the process and product consistency

方法:

At each stage, after the process has been given sufficient time to stabilise, a run of sixteen consecutive mouldings is to be made. These mouldings will be assessed for consistency by weight (a dimension, a physical property or some other attribute could equally well be used, weight is simply the most widely applicable).

稳定性通过计算重量的标准偏差来衡量. 同时打印出机床IBED上的过程统计数据.

1. 找出转压点

2. 找出浇口冷却时间 3. 优化注射速度

4. 采用正确的螺杆转速 5. 优化多级预塑曲线 6. 优化松推

7. 优化多级保压曲线 8. 优化锁模力

9. 设定注射压力限定

步骤 1

找出转压点

在没有保压压力和保压时间的基础上填满产品95% -98%, 然后设定一定的保压和保压时间生产16模.

初始设置时的指导

1 采用行程切换 2 设定切换位置为10-12mm (逐步增加预塑量直到产品打满95% - 98% 的位置) 3 设置注射压力为最大值 4 设定保压压力和保压时间均为0 5 设定注射速度 60 mm s-1 6 设定松推速度为最大值 7 设定锁模力为最大值 8 选择适当的螺杆转速 9 根据材料物性表, 设定料桶温度 10 配置过程统计控制 11 设定保压压力和保压时间生产完整的产品称12 模产品的重量, 计算标准偏差

打印:

页面 20 工艺参数优化页面 50 工艺过程统计

步骤 1 结果

输入实际值没保压时的重量平均值范围最小最大有保压后的重量填充的百分比标准偏差 (16 模) 料垫 (平均值和范围) 预塑时间 (平均值和范围)螺杆停止位置 (平均值和范围) 注射时间 (平均值和范围) 注射压力峰值, P inj. max 转压压力, PN press. 转压位置 % g 8

步骤 2

找出浇口冷凝时间

设定保压压力为步骤1 上找出的注射压力峰值的50% 左右.

设定保压时间为 1 s .

生产数模产品使过程稳定后连续取5模产品称出每模重量和平均值

增加保压时间至2 s, 生产数模产品使过程稳定后连续取5模产品称出每模重量.

在保压时间3s, 4s 5s . . . 时重复上述过程直到产品重量不再增加

作出产品重量和保压时间的关系图.

记录Record the TCU setting and the actual mould temperature.

打印:

页面 30 温度

XL Spreadsheet graph

为什么记录模具温度很重要

还有什么因素会影响浇口冷凝时间?

步骤 2 结果

输入实际值 TCU setting C 重量 1 重量2 重量3 重量4 重量5 平均重量时间保压 FH temperature C MH temperature C 重量1 重量2 重量3 重量4 重量5 平均重量时间保压所需的保压时间

s 10

步骤 3

优化注射速度

采用多级注射曲线, 使注射行程最后的10-20% 采用逐步降低的注射速度.

每次更改注射速度, 必须重新建立转压点. (注意每次保压和保压时间都设定为0.)

连续取16模, 计算出标准偏差.

打印:

页面 24 MWE 使用和没使用多级保压时的曲线页面 26 多级注射页面50 工艺过程统计

为什么转压点要更改

注射压力发生了什么?

为什么在数社的末端采用逐步降低的注射速度是有用的?

步骤 3 结果

输入实际值没有保压时的重量采用保压的重量填充百分比标准偏差 (16 模) 料垫 (平均值和范围)平均值范围最小最大预塑时间 (平均值和范围)螺杆停止位置(平均值和范围) 注射时间 (平均值和范围) 注射压力峰值, P inj. max 转压压力, PN press. 转换位置

% g

步骤 4

采用正确的螺杆转速

Select the correct, optimum screw speed for the material being processed (see T.01 notes, Section 5 ). Use this single speed for the whole plasticising stroke

Set a back pressure of 5 to 10 bar (hydraulic).

Readjust dosing stroke to achieve 95-98% fill

Take sixteeen consecutive mouldings and determine the standard deviation of the weights.

Print out:

Page 50 Process Statistics

Why is it important to use the manufacturer’s recommended screw speed?

STEP FOUR RESULTS

Insert actual values in the relevant boxes Weight without holding pressureWeight with holding pressure Percentage fill Standard deviation (16 shots) Mean value Rangeminmax Dosing time (mean and range) Melt cushion (mean and range)Screw stop position (mean and range) Injection time (mean and range) Peak injection pressure, P inj. max Injection pressure at changeover, PN press. Changeover stroke % g 14

STEP FIVE

Optimise screw speed and back-pressure profile

Use the Dosing Profile page to slow down the screw rotation speed for the last 10% of the metering stroke.

Readjust dosing stroke to achieve 95-98% fill

Take sixteeen consecutive mouldings and determine the standard deviation of the weights.

Print out:

Page 21 Dosing Profiles Page 50 Process Statistics

What has happened to the Dosing Stop position?

STEP FIVE RESULTS

Insert actual values in the relevant boxes Weight without holding pressureWeight with holding pressure Percentage fill Standard deviation (16 shots) Melt cushion (mean and range)Dosing time (mean and range)Mean value Rangeminmax %g Screw stop position (mean and range) Injection time (mean and range) Peak injection pressure, P inj. max Injection pressure at changeover, PN press. Changeover stroke 16

STEP SIX

Optimise decompression

Find the decompression speed which gives best screw stroke and melt cushion consistency. Set a decompression stroke of 5mm.

Check that you still achieve 95-98% fill.

Take sixteeen consecutive mouldings and determine the standard deviation of the weights.

Print out:

Page 21 Dosing Profiles Page 50 Process Statistics

What has happened to the screw stop position?

What is happening to the check ring?

STEP SIX RESULTS

STEP SEVEN

Optimise holding pressure profile

Use the Holding Profile page to set a holding pressure profile which ensures a smooth transition from injection to the holding pressure phase and use a high enough pressure to pack the part properly.

Add a step which reduces holding pressure gradually to zero.

Take sixteeen consecutive mouldings and determine the standard deviation of the weights.

Print out:

Page 24 MWE

Page 27 Holding Profile Page 50 Process Statistics

Why do you need a smooth transition from injection to holding pressure?

Why bother to reduce the pressure gradually if the gate has already frozen?

STEP SEVEN RESULTS

TABULATED RESULTS

Insert actual values in the relevant boxes

The range value, R, is the maximum minus the minumum, taken from the seven steps.

Melt cushion Dosing time Screw end position Injection time Injection pressure P hyd max Inection pressure PN hydraulic Changeover stroke Standard deviation (16 shots) 1 mean R 2 mean R 3 mean R 4 mean R 5 mean R 6 mean R 7 mean R

Can you see a trend?

Which step had the greatest effect on the consistency of the moulding?

STEP EIGHT

Optimising the clamp force

Reduce the clamp force by steps of 50 kN (100 kN for machines over 100 tonnes) using the settings far optimised in the seven steps above.

Allow the process to stabilise each time and then weigh five mouldings.

Tabulate your results below and plot a graph of tonnage against part weight.

Does the mould require the expected clamp force?

What are the advantages of running at reduced tonnage?

STEP EIGHT RESULTS

Insert actual values in the relevant boxes

Enter results in XL spreadsheet. Print out graph. Weight 1 Weight 2 Weight 3 Weight 4 Weight 5 Mean weight Clamp force Required clamp force kN 22

STEP NINE

Set injection pressure

Until now the injection pressure has been set to the machine’s maximum value. From the Process Statistcs page it can be seen that the machine does not need all that pressure to fill the mould.

Gradually decrease the set injection pressure until the injection time starts to increase. Increase the pressure again until the previous injection time is established with a consistency of 0.08 s or better – preferably 0.02 to 0.03 s variation.

What is the purpose of limiting the injection pressure?

STEP NINE RESULTS Actual peak injection pressure Set injection pressure bar bar 23

Appendix 1

TYPICAL PROCESS TOLERANCES

Shot-weight deviation Plasticising time Injection time Cycle time Screw position, dosing stop Melt cushion Melt temperature Mould temperature Barrel temperature Feed zone temperature Hot runner temperature Hydraulic oil temperature Room temperature Mould cavity pressure Pressure integral Injection filling pressure Holding pressure Back pressure Filling differences (Balance of fill for each cavity) on multi-cavity tools Mould breathe Change over pressure (Pn Value) Screw surface speed Melt temperature peak value Melt temperature value at changeover 0.05% ± 0.04s ± 0.02s ± 0.5% ± 0.1mm ± 0.1mm ± 2°C ± 1°C ± 1°C ± 1°C ± 1°C ± 1°C ± 2°C ± 3 bar ± 200 ± 1 bar ± 1 bar ± 0.5 bar ± 1% 0.01mm ± 1 bar ± 10mms-1 ± 0.3ºC ± 0.3ºC 0.1% ± 0.06s ± 0.02s ± 0.5% ± 0.1mm ± 0.1mm ± 2°C ± 1°C ± 1°C ± 2°C ± 2°C ± 1°C ± 2°C ± 4 bar ± 300 ± 2 bar ± 1 bar ± 0.5 bar ± 1% 0.01mm ± 2 bar ± 15mms-1 ± 0.4ºC ± 0.4ºC 0.2% 0.08s ± 0.04s ± 1% ± 0.2mm ± 0.2mm ± 3°C ± 2°C ± 2°C ± 3°C ± 3°C ± 2°C ± 3°C ± 6 bar ± 600 ± 3 bar ± 1.5 bar ± 1 bar ± 2% 0.02mm ± 3 bar ± 20mms-1 ± 0.5ºC ± 0.5ºC 0.4% 0.13s ± 0.06s ± 1% ± 0.3mm ± 0.3mm ± 5°C ± 4°C ± 4°C ± 4°C ± 4°C ± 2°C ± 4°C ± 8 bar ± 900 ± 4 bar ± 2 bar ± 1 bar ± 5% 0.04mm ± 4 bar ± 30mms-1 ± 0.6ºC ± 0.6ºC The achievable part quality is much influenced by the condition of the material processed.

It is important that moisture content, proportion of regrind and proportion of colour (masterbatch) are constant.

Acceptable tolerances of principal injection moulding processing

parameters

Bichler:Abt 9601- May 88 Updated Feb 01

Appendix 2

Standard deviation

Standard deviation is a measure of the spread or scatter in a process and for a sample is given by the equation below:

where

 standard deviation(xx)ii1in2n1

 the sum of the differencesxithe individual value

xthe mean valuenthe number of values

The spread of a process may be estimated from the range, R . The maximum value minus the minimum. The smaller the range, the less spread in the process.

A more sophisticated way of estimating scatter, which is widely used for statistical process control is standard deviation, , which not only provides a measure of the

precision of the process, but also predicts how many parts in a population will be out of tolerance.

For what is known as a normal distribution, 68.3% of the population will lie within one standard deviation above and below the mean, 1 ; 95.4% lie within 2, 99.7% within 3 and 99.994 within 4.

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