This lecture describes the basic methods of quality assurance and process control for mechanical fastening methods. General mechanical engineering background and familiarity with the subject matter covered in TALAT This lectures 4101- 4105 is assumed.

1. TALAT Lecture 4106
Quality Assurance and Process Control
9 pages, 8 figures
Basic Level
prepared by Lothar Budde, Universität-Gesamthochschule Paderborn
Objectives:
− to descibe the basic methods of quality assurance and process control for mechanical
fastening methods
Prerequisites:
− General mechanical engineering background
− TALAT lectures 4101 - 4105
Date of Issue: 1994
 EAA - European Aluminium Association

2. 4106 Quality Assurance and Process Control
Table of Contents
4106 Quality Assurance and Process Control..................................................2
4106.01 Process Analysis .......................................................................................... 3
Comparison of Quality Assurance of Different Joining Technologies ....................3
Direct Process Control as a Supplement to Statistical Process Control...................3
Path of a Mechanical Fastening Process ..................................................................4
4106.02 Controlling Process Parameters .............................................................. 5
Characteristic Deformation Diagram of a Blind Rivet ............................................5
Controlling the Limiting Values for Mechanical Fastenings...................................6
Characteristic Force-Motion Studies for Clinching with Local Incision .................6
Cross-Section of a Clinch Joint with Characteristic Values for Joint Geometry.....7
Example of a Process Analysis for Clinch Joints with Local Incision ....................8
4106.03 Literature/References .............................................................................. 9
4106.04 List of Figures.............................................................................................. 9
TALAT 4106 2

3. 4106.01 Process Analysis
• Comparison of quality assurance of different joining technologies
• Direct process control as a supplement to statistical process control
• Path of a mechanical fastening process
Comparison of Quality Assurance of Different Joining Technologies
The predictability of mechanical fastenings in the production technology depends
largely on the reproducibility of the joint, which, in turn, is correlated to the tolerance of
the production process.
Contrary to the combined adhesive and spot welded fastening, clinched and self-piercing
riveted joints - as typical examples of mechanical joining methods - can, to a certain
extent, be tested using non-destructive testing methods (Figure 4106.01.01).
Joining
Technology Adhesive Spot Welding Clinching Riveting
Characteristics Joining
Quality Assurance Process Control Process Control Process Control Process Control
Possible Only Only Conditionally Only Conditionally Only Conditionally
in Partial Steps Possible Possible Possible
Joint cannot Joint cannot Joint can be Joint can be
be Tested Non- be Tested Non- Tested Non- Tested Non-
Destructively Destructively Destructively Destructively
Conditionally Conditionally
Source: Budde
Comparison of Quality Assurance of Different
alu
4106.01.01
Training in Aluminium Application Technologies Joining Technologies
Direct Process Control as a Supplement to Statistical Process Control
It has often been pointed out here that the quality assurance of mechanical fastenings for
aluminium constructions is of paramount importance. With automation it is possible to
eliminate the influence of random and chronologically limited personal errors on the
quality of the fastening. Supplementary to the destructive and non-destructive testing of
samples, the process control and regulation of the mechanical fastening process offers a
promising additional quality assurance method.
The direct process regulation and control based on the relevant data extracted during the
actual joining process - i.e. in addition to the statistical process control - plays an
important role in the mechanical fastening process (Figure 4106.01.02).
TALAT 4106 3

4. Rivet Element
Riveting Process
Jointing Parts Riveted Joint
In-Process Post-Process
e.g. e.g.
Force Rivet Element
Path Formation
(Random Sample)
Statistical
Process
Process
Control
Control
Source: Budde
Direct Process Control as a Supplement to
alu
4106.01.02
Training in Aluminium Application Technologies Statistical Process Control
Path of a Mechanical Fastening Process
The force-motion analysis builds the basis of the direct process control and regulation of
mechanical fastening (see Figure 4106.01.03). Based on process analysis, it is possible
to follow the mechanical joining process qualitatively and, at the same time, to
determine the quantitative correlation existing between the relevant chronological
changes in the joining process and the quality of the joint produced, whereby the term
quality is defined as the joint strength at varying loads.
The operational path of the mechanical fastening process illustrates that the process
control and regulation is based on the determination of the actual current geometrical
formation and on the assumption that each joint geometrical form (evaluated on the
basis of the geometric joint characteristics) has an individual defined quality.
Joining Process
Analysis Characteristic
Observed Process Index
Variable of State
Force
Path
Process Steps Form of Joining Mech. Behaviour
of Joining Element of Joint
Force
d
N hN
Path
Uncontrollable
Input Variables
Not Observed Characteristic
Controllable Variables of State Joint Values
Input Variables
Source : Budde
alu
Path of a Mechanical Fastening Process 4106.01.03
Training in Aluminium Application Technologies
TALAT 4106 4

5. 4106.02 Controlling Process Parameters
• Characteristic deformation diagram of a blind rivet
• Controlling the limiting values for mechanical fastenings
• Characteristic force-motion studies for clinching with local incision
• Cross-section of a clinch joint with characteristic values for joint
geometry
• Example of a process analysis for clinch joints with local incision
Characteristic Deformation Diagram of a Blind Rivet
Blind riveting (mechanical fastening with auxiliary parts) and clinching (mechanical
fastening without auxiliary parts) are processes for which process control and
regulations have been applied (Figure 4106.02.01).
The process steps during blind riveting can be divided into a in-slippage phase (in which
the stem is pulled) and a clamping phase (in which the fastening parts are subject to a
pre-stress).
The clamping force and consequently the quality of the riveted joint can be
predetermined by analysing the deformation diagram for blind riveting.
3
Breaking Force for
Rivet Mandrel
Forming Force [kN]
2 Clamping Phase
1
Inslippage Phase
0
0 2 4 8 10
Source: Budde Forming Path [mm]
alu
Characteristic Deformation Diagram of a Blind Rivet 4106.02.01
Training in Aluminium Application Technologies
TALAT 4106 5

6. Controlling the Limiting Values for Mechanical Fastenings
At the end of the process analysis of the mechanical joining process, one has to decide
whether the quality requirements can be reliably fulfilled or whether a direct process
control has to be carried out continuously. During a process control, the characteristic
joint values are determined and constantly evaluated. On the basis of the process
analysis, it is possible to develop appropriate control strategies like, for example, a
control of the limiting values (Figure 4106.02.02).
Evaluation : Evaluation :
Joint in Good Condition! Joint With Flaws!
Force Force
Path Path
Source: Budde
Controlling the Limiting Values for
alu 4106.02.02
Training in Aluminium App licatio n Technologies Mechanical Fastenings
Characteristic Force-Motion Studies for Clinching with Local Incision
Just as in the case of self-piercing riveting, it is possible to use force-motion diagrams to
study the individual phases of the joining process during clinching (Figure 4106.02.03).
Experiments have shown that the joint force determined point-wise (locally) or
interactively can be treated as a universal control parameter. The chronological change
of the joining force offers very significant information about the process and the
forming of the joint.
TALAT 4106 6

7. Multi-Step CL
Single-Step Clinching (CL)
with an Eccentric Press
with Hydraulic C Press
Dependent on Path
Cutting
Die
Compression (SM)
and Further Incision
S SM Press
Clinching Punch
and Cutting
(DS)
2
Joining Force F
Punch Force F
1
S DS
3
7 8 9 FF
Punch Path Ss Angle of Crank
Source: Budde
Characteristic Force-Motion Studies for Clinching
alu
4106.02.03
Training in Aluminium Application Technologies with Local Incision
Cross-Section of a Clinch Joint with Characteristic Values for Joint Geometry
Two types of characteristic values exist for the joint geometry, depending on whether
these values can be measured with or without destroying the joint element. It has been
found that for clinch joints, a linear correlation exists over a large range among the
joining process dependent values of web thickness, web breadth and the joint strength.
Consequently, the web thickness and/or breadth are used to optimise the joint and for
non-destructive testing of the same (see also Figure 4106.02.04).
3
mm
Web Thickness ST / Penetration Depth ET
6
mm
ET
2
B
5
Web Width B
ET
1
ST ST
B 4
0 0
Joining Force F
Source: Budde
Cross-Section of a Clinched Joint with
alu
4106.02.04
Training in Aluminium Application Technologies Characteristic Values for Joint Geometry
TALAT 4106 7

8. Example of a Process Analysis for Clinch Joints with Local Incision
Through the control of the joining force, it is possible to control every clinching or
punch riveting process quasi on-line. Thus it is possible, for example, to clearly
recognise different damages of the die during the single-step clinch process by studying
the force-time curve (Figure 4106.02.05).
28 Single-Step Clinching (with Local Incision)
of Shaped Sheet Parts
kN
20
Joining Force
16
Expected Curve
12
8
Damage to Anvil
4
0 Damage to Spring Lamella
0 0,05 0,1 0,15 0,2 0,25 sec 0,35
Time
Source: Bober, Liebig
Example of Process Analysis for Clinch Joints
alu
with Local Incision 4106.02.05
Training in Aluminium Application Technologies
This makes it possible to evaluate the quality of mechanical joints in aluminium shaped
sheet and profile products using non-destructive methods.
Although the process control during riveting and clinching makes it possible to
guarantee the joint quality control of the mechanical fastening process, it is still
necessary to collect comprehensive data if one wants to be able to influence the design
of the aluminium construction within the framework of a more global quality assurance.
TALAT 4106 8

9. 4106.03 Literature/References
1. Budde, L. Untersuchungen zur Kombination quasi-formschlüssiger und
stoffschlüssiger Verbindungsverfahren. Dissertation Uni-GH-Paderborn, 1989
2. Schmid, G. Methoden der Qualitätssicherung beim Durchsetzfügen. Bänder Bleche
Rohre 32 (1991) 61-64
3. Budde, L. Qualitätssicherung beim Nieten - Möglichkeiten und Grenzen. Bänder
Bleche Rohre 32 (1991) 64-74
4. Liebig, H.P. und Mutschler, J. Qualitätssicherung beim Stanznieten
prozeßbegleitend überwachen. Bänder Bleche Rohre 34 (1993) 5, 52-54
5. Warnicke, H.-J. und Schweizer, M. Bleche sicher verbinden - Automatische
Nietprozeßüberwachung. Wissenschaft und Technik. Springer Verlag (1993) 1, 50-
52
6. Lappe, W. und Budde, L.Qualitätsbewußt - Möglichkeiten der
Prozeßüberwachung beim Stanznieten von Blechen und Profilen. Maschinenmarkt
99 (1993) 48, 60-64
7. Liebig, H.P., Bober, J. und Göpfert, D. Qualitätssicherung durch
rechnerunterstützte Überwachung des betrieblichen Druckfügeprozesses. Blech
Rohre Profile 39 (1992) 6, 466-471
4106.04 List of Figures
Figure No. Figure Title (Overhead)
4106.01.01 Comparison of Quality Assurance of Different Joining Technologies
4106.01.02 Direct Process Control as a Supplement to Statistical Process Control
4106.01.03 Path of a Mechanical Fastening Process
4106.02.01 Characteristic Deformation Diagram of a Blind Rivet
4106.02.02 Controlling the Limiting Values for Mechanical Fastenings
4106.02.03 Characteristic Force-Motion Studies for Clinching with Local Incision
4106.02.04 Cross-Section of a Clinched Joint with Characteristic Values for Joint Geometry
4106.02.05 Example of Process Analysis for Clinch Joints with Local Incision
TALAT 4106 9