Cmk calculation - Small plastic parts using injection-moulding machine

M

Marcin

#1
Hi,

We manufacture small plastic parts using injection-moulding machine. There are quite big batches of production (average 50 000 parts per lot). Please advise me how we should calculate Cmk factor:
1. When it should be calculated (once a year or may be after each new connection of injection-moulding machine with the tool (mould))?
2. How many samples must be taken (I assume that 1 sample always consists of 5 parts)?
3. How frequently samples must be taken?

Thanks in advance.
 
Elsmar Forum Sponsor
D

Don Winton

#2
I do not a lot of experience in Machine Capability studies, but I took this from http://www.autotrain.org - Link was: /auto-home/main.html

Capability - Machine Capability

A Machine Capability Study is not, strictly speaking, part of Statistical Process Control, as it does not detect the presence or absence of special causes. Instead, it provides a "snapshot" of one particular component of a process, often a machine (hence the title). This could well be of use in the context of, for example, carrying out a trial run on a machine before agreeing to buy it (like test driving a car).

A Machine Capability Study is essentially a way of establishing the capability of the component/machine by assessing how it operates:
  • over a very short period of time
  • in an ideal environment

By an ideal environment, we mean one in which:
  • the machine is set as close as possible to its optimum values
  • it is being operated by an experienced member of staff
  • it is isolated from the normal working environment (and thus unlikely to be affected by special cause variation)
  • the study takes place over a very short period of time

Typically, about 50 outputs of the process would provide data for a Machine Capability Study. This may vary depending on the outputs. For example, an hour's output of nails might be more than enough, whereas producing 50 back axles might not be practical.

Regards,

Don
 
R

Roger Eastin

#3
I'm not sure what a "Cmk" is, either. Does "m" stand for machine? If it does, then Don probably has the right conditions listed. However, if it is a standard process capability study, you must establish that special causes have been eliminated before you calculate the capability index. Otherwise, you get into questions of things like normality and its impact on percent of product out of spec. Perhaps could describe what you are trying to do in a little more detail.
 
Thread starter Similar threads Forum Replies Date
F MCA calculation - problem with Cm Cmk and boundaries Capability, Accuracy and Stability - Processes, Machines, etc. 1
M How is the Cmk and Cpk calculated? Statistical Analysis Tools, Techniques and SPC 0
G Function in french called "numbre de posage(s)" - CMK Question Quality Tools, Improvement and Analysis 3
K Excel Spreadsheet Template to calculate Cmk (Machine Capability) wanted Capability, Accuracy and Stability - Processes, Machines, etc. 2
Q Machine Capability Study - Cpk (Cmk) of an R/F testing machine Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
L Fastening Process Cmk study - Bolt Torque Statistical Analysis Tools, Techniques and SPC 1
L Multi-fixtures in one CNC lathe - How to do Cmk study? Statistical Analysis Tools, Techniques and SPC 6
M Cmk (Machine Capability) - Case study Capability, Accuracy and Stability - Processes, Machines, etc. 5
C Gauge R&R Studies Bad, but Process has a Cmk of over 7 IATF 16949 - Automotive Quality Systems Standard 8
S A question about Cpk and Cmk - Can we use Cpk to replace Cmk? Capability, Accuracy and Stability - Processes, Machines, etc. 1
V Machine short term capability study with Cmk index in automotive industry Capability, Accuracy and Stability - Processes, Machines, etc. 3
Q Confused about the machine capability index Cmk Capability, Accuracy and Stability - Processes, Machines, etc. 1
D Tool Approval Process - Should we be using Cmk for tool validation Statistical Analysis Tools, Techniques and SPC 2
A Acceptance criteria for Cmk (machine capability index) Statistical Analysis Tools, Techniques and SPC 3
H Some questions about Cmk and Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 2
B I am confused, which Cmk value should I take and use? Statistical Analysis Tools, Techniques and SPC 6
M How to Conduct a Machine Capability (Cmk) Study Statistical Analysis Tools, Techniques and SPC 26
C Evaluating software that measures Ppk, Cmk, Cpk, PPI, etc. Capability, Accuracy and Stability - Processes, Machines, etc. 4
S Cmk and Cpk - When will we need to calculate Cmk? Machine Capability Capability, Accuracy and Stability - Processes, Machines, etc. 4
A Cpk, Cmk in Electronic Assembly (Process Capabiity) Capability, Accuracy and Stability - Processes, Machines, etc. 4
S Cmk is defined as a Capability Index for a Stable Machine Capability, Accuracy and Stability - Processes, Machines, etc. 8
B Any ideas on setting up Capability Study spreadsheet in Excel? (CPK/CMK formulae) Excel .xls Spreadsheet Templates and Tools 4
K Cmk - What is the difference between an R&R study and Cmk? Statistical Analysis Tools, Techniques and SPC 4
D Can anyone enlighten me as to what exactly Cm / Cmk are? Statistical Analysis Tools, Techniques and SPC 1
S Cost of Poor Quality (CoPQ) - Scrap element of calculation includes lost margin? Misc. Quality Assurance and Business Systems Related Topics 7
K Analysis variation among the lots during cpk calculation. Design and Development of Products and Processes 1
0 PPM calculation of customer complaints for PMS Customer Complaints 10
T Overvoltages consideration in Applied Part for RMS Calculation. IEC 60601 - Medical Electrical Equipment Safety Standards Series 6
U Cpk Calculation - I analyse a double seam cans Manufacturing and Related Processes 15
I Lifetime Support Calculation - Thermal Operating Profile Reliability Analysis - Predictions, Testing and Standards 7
Q Stock Reorder point calculation Lean in Manufacturing and Service Industries 1
G 3 Operator Std. Dev. and uncertainty calculation Measurement Uncertainty (MU) 2
F Determining what type of scrap to include in my internal PPM calculation Quality Manager and Management Related Issues 5
F Holes position inspection - Calculation of centre distance and plug sizes of a gauge Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
P Any official doc/spec on different types of Yield calculation? Manufacturing and Related Processes 0
M Benchmarking Process Data - Man-day calculation gone wrong Benchmarking 5
H Taguchi mixed model DoE [L16 (4^3 2^6): factors interaction and ANOVA calculation Using Minitab Software 3
L P-Chart Control Limit Calculation help Statistical Analysis Tools, Techniques and SPC 1
H Sample Size Calculation (Confidence Interval and Reliability) - Medical Devices Reliability Analysis - Predictions, Testing and Standards 6
E Questions regarding Cpk Calculation - Should we be using LSL/USL or LCL/UCL? Capability, Accuracy and Stability - Processes, Machines, etc. 5
L Number of Distinct Categories" or NDC Calculation in MSA Studies Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
V Sample Size Calculation for Image Analysis - Microscopy Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
Q Rule 5.2h - Site Separation - Audit Manday Calculation (IATF 16949) IATF 16949 - Automotive Quality Systems Standard 17
kedarg6500 Gage R&R - Is my sheet calculation wrong? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 21
C Practical use of Heat Input calculation for Manual MIG Welding Manufacturing and Related Processes 4
J CMM Uncertainty Calculation Question - Deviations Measurement Uncertainty (MU) 9
S Scrap % Calculation Formula Manufacturing and Related Processes 10
T Reliability calculation for repairable system Reliability Analysis - Predictions, Testing and Standards 14
F Calculation of reduction on audit time - IAF MD1:2007, IAF MD5:2015 and IAF MD11:2013 General Auditing Discussions 1
Mikael Is there a calculation in Net Promoter Score (NPS) ? Statistical Analysis Tools, Techniques and SPC 3
Similar threads


















































Top Bottom