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Cold Micro Metal Forming

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Nguyễn Gia Hào

Academic year: 2023

Chia sẻ "Cold Micro Metal Forming"

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Michael Lütjen BIBA – Bremer Institut für Fertigung und Logistik GmbH, Universität Bremen, Bremen, Deutschland. Daniel Rippel BIBA – Bremer Institut für Fertigung und Logistik GmbH, Universität Bremen, Bremen, Deutschland.

Motivation

A typical example of the advantages and challenges of miniaturization is the ABS (anti-lock braking system) in modern cars. This is often not only due to cost, but also due to the critical safety of many components (ABS, medical devices).

Aim of the SFB 747

Structure and Partners

At the beginning of the interacting processes is the production of semi-finished products for the production of micro-design. Microstructuring of polycrystalline diamond (Dr. Yiqing Chen and Prof. Liagchi Zhang from the University of New South Wales, Australia).

Table 1.1 Project Structure of the Collaborative Research Center (SFB 747). Line 1: DFG Short number and title, Line 2: Running Head(s) of the project, Line 3: Duration of the project (start and end), Line 4: Link for further details
Table 1.1 Project Structure of the Collaborative Research Center (SFB 747). Line 1: DFG Short number and title, Line 2: Running Head(s) of the project, Line 3: Duration of the project (start and end), Line 4: Link for further details

Main Results .1 Innovation Speed

Micro Mass Forming

Thus, the development of robust micro cold forming processes presupposes an understanding of friction and wear mechanisms in the micro regime. It should be considered in all components of the microprocessor chain (see Fig.1.6).

Fig. 1.6 Dispersion affects all components of a production process, the geometric or material properties of the workpiece, the process capability, the measuring process, and fi nally propagates to the quality features of the micro part
Fig. 1.6 Dispersion affects all components of a production process, the geometric or material properties of the workpiece, the process capability, the measuring process, and fi nally propagates to the quality features of the micro part

Mastered Production

However, the challenge is to determine the tool wear from a measurement of the mold product. Using an experimental determination of the solidification speed (Sect.2.2), the expected transport mechanisms for the heat transfer were validated.

Introduction to Micro Forming Processes

One effect of the reduced micro part formation rate is relatively closer tolerances for manufacturing. Numerical methods and experimental research allow the detection of geometric influences and their individual contribution to work quality and process stability.

Generation of Functional Parts of a Component by Laser-Based Free Form Heading

Laser Rod End Melting

Here, the energy balance and solidification affect the reproducibility and microstructure of the preform. During masterforming, the eccentricity of the preform relative to the bar is determined.

Fig. 2.1 Upsetting a multi-stage process conventional upsetting, b alternative process laser-based free form heading with only two process stages [Br ü 16b]
Fig. 2.1 Upsetting a multi-stage process conventional upsetting, b alternative process laser-based free form heading with only two process stages [Br ü 16b]

Laser Rim Melting

Here, a shear stress of 69 N/cm2 can be transmitted by a metal hook-and-loop fastener [Brü14c]. The wide range of possibilities for the laser-based freeform routing process, which is extended from ingots to sheets, is appreciated so that more new applications can be exploited and industrial integration is expected.

Fig. 2.12 Continuous preform on a metal sheet with a thickness of 70 l m: a cylindrical, b irregular [Sch17c]
Fig. 2.12 Continuous preform on a metal sheet with a thickness of 70 l m: a cylindrical, b irregular [Sch17c]

Rotary Swaging of Micro Parts

  • Introduction
  • Process Limitations and Measures for Their Extension
  • Material Flow Control
  • Characterization of the Material Flow with FEM
  • Material Modi fi cations
  • Applications and Remarks

In low-rotational lowering, the deformed volume of the workpiece is assumed to have a cylindrical shape. Due to the incomplete closure of the dies, the final diameter of the workpiece increases. The spread of the Martens hardness after forming (range I to IV and the beginning of V) reaches up to 250 N/mm2 compared to about 160 N/mm2 before forming (the end of range V).

Fig. 2.15 Front view of a rotary swaging machine without end cover
Fig. 2.15 Front view of a rotary swaging machine without end cover

Conditioning of Part Properties

Introduction

Micro-input rotary swing not only changes the geometry and the surface of the forged parts, but also affects the microstructure and therefore the mechanical properties of lubricated workpieces. Due to the special adaptations of the machine, it was possible to change the manufactured diameter [Kuh13] and the roughness of the swung parts [Ish15c]. They concluded that rotary lubrication can provide the opportunity to adjust the forming properties of the workpieces for further forming steps [Ish15a].

Process Chain “ Rotary Swaging — Extrusion ”

Further increase of the shear stress in the workpiece was achieved by eccentric rotational oscillation. In the case of the same speed of rotation of the workpiece and flat-shaped grains, the angle after impact Δ/ is equal to zero and the dies touch the workpiece all the time in the same circular line (Fig. 2.36a). For a comparison of forming characteristics, "NS" (non-swaged) samples at the initial stage are turned from non-swaged parts.

Fig. 2.34 Distribution of the shear strain PE12 at the end of the reduction zone
Fig. 2.34 Distribution of the shear strain PE12 at the end of the reduction zone

Results and Discussion

Although flat-shaped dies allow a significant reduction in yield stress [Ish17b,Ish15a] and hardening, increasing the feed rate from vf= 1 mm/. The roughness of the workpieces pressed with flat dies was well influenced by the feed speed vfas during pressing (reduced to Sa= 0.94±0.23lm). The use of flat tools or double flat tools in combination with the target setting of the pursuit angle Δ/supplied polygonal shaped parts with multiple faces.

Fig. 2.38 Characterization curves based on tool design. I: curve-shaped dies (CSD), II:
Fig. 2.38 Characterization curves based on tool design. I: curve-shaped dies (CSD), II:

In fl uence of Tool Geometry on Process Stability in Micro Metal Forming

Introduction

In conventional deep drawing processes, manufacturing deviations in the sub-millimeter range in tools do not affect the deep drawing process, as these deviations are negligible in size compared to the dimensions of the tool. This is due to the relative deviations of the tool geometry, which are caused in the manufacture of tools. Therefore, the aim of this study is to determine the influence of tool geometry on microforming processes to allow a specific process design and improved process stability, as well as a quantitative assessment of the effect of wear- and production-related deviations of tool geometry.

Experimental Setup

Thus, the quality of manufactured parts depends on the selection of appropriate geometrical parameters of the forming tools. The corresponding geometric parameters of the tools used in the experiment were measured with a Keyence VK 9700 laser scanning microscope. With this setup, the blanks can be placed within a radius of 10 µm from the center of the drawing die.

Numerical Models

Piston stroke was measured with a Heidenhain LS477 linear scale with an accuracy of 1 lm. The workpiece was placed with a pneumatic gripper driven by a linear direct drive cross table. The position of the blank was then measured using an Allied Vision G 917 B monochrome CCD camera with a resolution of 9 MP equipped with a telecentric lens with built-in coaxial illumination and a magnification of 0.75.

Circular Deep Drawing

In [Beh16], the influence of raw material variation and tool geometry on LDR is described. Between these zones, the thickness of the cup wall is in the range of the initial thickness of the blank. Therefore, the influence of setting the die diameter D2 on the maximum impact force Fp,maxis is shown in Figure 2.54.

Figure 2.47 shows that the change of punch diameter and drawing gap resulted in the greatest impact on the punch force and therefore should be carefully  con-trolled during tool manufacturing
Figure 2.47 shows that the change of punch diameter and drawing gap resulted in the greatest impact on the punch force and therefore should be carefully con-trolled during tool manufacturing

Deep Drawing of Rectangular Parts

The influence of tool geometry deviation on punching force in rectangular microdeep drawing has been investigated in Behrens et al. Increasing the corner radius or decreasing the die radius has been shown to increase the resulting punch force and therefore have a negative effect on the drawing process. In addition, the results show that the influence of a die radius variation on the punching force is much more prominent in rectangular deep drawing compared to the formation of circular parts, which can be explained by the different composition of the punching force.

Forming Limit

Change of Scatter

Proceedings of the 4th International Conference on Nanomanufacturing (nanoMan 2014), pp. Brü14c] Brüning, H., Vollertsen, F.: Mit dem Laser zum Klettverschluss. Hu11] Hu, Z., Vollertsen, F.: Investigation of workpiece shape optimization for micro-engraving of rectangular parts. Kuh08b] Kuhfuss, B., Moumi, E., Piwek, V.: Influence of the feed rate on the work quality of microrotational sinking.

Fig. 2.56 Forming limit diagram and the lower forming limit curves for different foil materials
Fig. 2.56 Forming limit diagram and the lower forming limit curves for different foil materials

Introduction to Process Design Claus Thomy

This reduces the effort in handling and storage (both long-term storage and highly dynamic buffering), but increases the effort in referencing parts by their position and orientation at high production rates.

Linked Parts for Micro Cold Forming Process Chains

Introduction

Examples of the industrial application of production as connected macro parts are mainly found in the production of sheet metal parts by punching, bending and deep drawing. In combination with connecting the parts, micro-specific planning methods are also required. The main focus of the second field of research is on the production of connected parts.

Fig. 3.1 Considered process chains
Fig. 3.1 Considered process chains

Design and Production Planning of Linked Parts

The flow of forces during transportation of the connected parts flows through the parts themselves. Especially the border areas for the ladder-connected parts could be used for this [Week14]. The diameter of the parts is used to calculate the Euclidean distance [Tra18].

Fig. 3.3 Examples of the design of the border area of ladder-linked parts for absorbing forces
Fig. 3.3 Examples of the design of the border area of ladder-linked parts for absorbing forces

Automated Production of Linked Micro Parts

An example is illustrated in Fig. 3.8 through the production of parts connected to the investigated line. However, deviations of the shape of the connected parts from the desired geometry can result in directional inaccuracy. A change in the structure of the connected parts is especially noticeable in the case of mass formation.

Figure 3.9 illustrates the standard deviation of a measurement of the distance a between parts at different velocities compared to a reference measurement
Figure 3.9 illustrates the standard deviation of a measurement of the distance a between parts at different velocities compared to a reference measurement

A Simultaneous Engineering Method

Introduction

Companies need tools and methods for highly accurate planning that spans the entire process chain in order to cope with the phenomenon of the size effect. To facilitate the design and configuration process, this chapter presents the "Microprocess Design and Analysis" methodology, which was designed to support process designers with a tool to design and configure manufacturing process chains with the required level of detail. These causal networks combine expertise with methods from statistics and artificial intelligence to handle size effects.

Process Planning in Micro Manufacturing

Consequently, the design and configuration of process chains is considered a major success factor for the industrial production of metal micromechanical components [Afa12]. In micromanufacturing, small differences in individual parameters or characteristics can have a significant impact along the process chain and can ultimately hinder compliance with the relevant tolerances [Rip14]. The methodology itself offers tools and methods for modeling, configuration and evaluation of process chains in micro production.

Micro-Process Planning and Analysis ( µ -ProPlAn)

The third view focuses on the configuration of processes and process chains using so-called cause-effect networks. Since the cause-effect networks and the material flow elements are closely connected, µ-ProPlAn reflects changes in the configuration of the material flow simulation and evaluates these e.g. While the application of the described methods enables the cause-effect networks to predict the estimated (mean) value of a parameter, they do not support.

Fig. 3.19 Components of the µ -ProPlAn Methodology [Sch13]
Fig. 3.19 Components of the µ -ProPlAn Methodology [Sch13]

Introduction to Tooling

Like the work in Section 4.4, the work in Section 4.6 was done together with industrial partners, with a separate problem to solve. Section 2.4 (Conditioning of part properties) and Section 5.3 (Inspection of functional surfaces on micro-components inside cavities). The challenge in the work shown in Section 4.6 was to develop a method for optimized toolpaths independent of the actual machine tool.

Increase of Tool Life in Micro Deep Drawing

  • Introduction
  • De fi nitions
  • Experimental Setups
  • Measurement Methods
  • Materials
  • Results

Therefore, the comparison of tool wear is analyzed with a confocal microscope before and after several cycles of deep drawing [Hu10]. Flakes can be detected on the surface of the blanking and deep drawing cover with an EDX analysis. Thus, tool life in a combined dry blanking and deep drawing process is largely dependent on the removal of flakes.

Fig. 4.1 Principle of the experimental setup for a ball-on-plate test
Fig. 4.1 Principle of the experimental setup for a ball-on-plate test

Controlled and Scalable Laser Chemical Removal for the Manufacturing of Micro Forming Tools

Process Fundamentals

The locally induced temperature gradients result in the generation of a thermal battery, enabling a current to flow in the metal between the center of the incident laser light and its periphery. Yav94], it has been reported that the formed bubbles lead to removal disturbances that hinder the controllability of the LCM process [Meh13]. Figure 4.20 shows a schematic representation of the effect of adhering boiling gas bubbles on the LCM process.

Fig. 4.19 Schematic illustration of the relevant parameters and the dominant induced factors in laser chemical machining
Fig. 4.19 Schematic illustration of the relevant parameters and the dominant induced factors in laser chemical machining

LCM Machines Concepts

Depending on its size and dynamics, the bubble affects the amount and distribution of the deposited laser energy differently. The adhesive bubble can act as a scattering center and deflect part of the incoming laser beam to its periphery (light deflection effect). One of the main challenges in chemical laser machining is to ensure a controllable and homogeneous deposition of laser energy on the workpiece, considering

Fig. 4.21 Schematic illustration of the main components of the electrolyte-jet based LCM machine (JLCM)
Fig. 4.21 Schematic illustration of the main components of the electrolyte-jet based LCM machine (JLCM)

In fl uence of the Process Parameters on the Material Removal

Although different absorption coefficients, laser spot sizes and laser powers, the removal results show a strong dependence on the effective absorbed laser power Pabs as well as a negligible influence of the laser wavelength. A further increase of the laser power (above the boiling point of the electrolyte) results in removal disturbances [Meh13]. Furthermore, it turns out that the appropriate lateral overlap is dependent on the removal width of a single path and on the material used [Mes18a].

Fig. 4.23 Comparison between the LCM removal velocities and the background etching velocity of high-speed tool HS10-4-3-10 in 5 molar H 3 PO 4 solution in dependence on the interaction time
Fig. 4.23 Comparison between the LCM removal velocities and the background etching velocity of high-speed tool HS10-4-3-10 in 5 molar H 3 PO 4 solution in dependence on the interaction time

Strategies Towards a Controllable Laser Chemical Machining

In the thermal modelling, the influence of the electrolyte is considered through the transmission coefficients E and the heat transfer coefficient H. Due to the effective thermal energy distribution, the removal cross-section of the machined geometry is assumed to be a superposition of single Gaussian curves. The shape deviations of the manufactured micromatrices from the desired geometry have thus been shown to be significantly reduced with the developed quality control.

Table 4.2 List of process parameters used for both modeling and experimental investigation
Table 4.2 List of process parameters used for both modeling and experimental investigation

Tool Fabrication

Figure 4.30 shows examples of the captured SEM images of laser chemically roughened and finished microcavities with the target dimensions of (30030060)µm3. LCM roughing mainly results in the achievement of the cavity dimensions, while LCM finishing provides the final contouring and smoothing of the cavity surface. Figure 4.31a shows the CRC 747 logo with a pattern of the various square cavities in Stellite 21.

Table 4.4 List of the symbols used
Table 4.4 List of the symbols used

Comparison with Other Micro Machining Processes

However, the final quality of micro-milling with a medium surface roughness of Saof 0.2 lm could not be achieved by laser chemical processing. Based on tool surface, the average removal rates under the machining conditions used are 2.710−5mm3/min for LCM and 6.7510−5mm3/min for micromilling. Overall, the presented examples demonstrate the diversity and flexibility of laser chemical processing and its performance, which is comparable to established processes such as micro-milling and ECM.

Fig. 4.33 Top view SEM images of a micro milled (above) and laser chemically machined (below) cavity with targeted dimensions of (150  150  60) l m 3 as well as under 60 ° magni fi ed sections showing the cavity wall
Fig. 4.33 Top view SEM images of a micro milled (above) and laser chemically machined (below) cavity with targeted dimensions of (150 150 60) l m 3 as well as under 60 ° magni fi ed sections showing the cavity wall

Process Behavior in Laser Chemical Machining and Strategies for Industrial Use

  • Introduction
  • Materials and Methods
  • Sustainable Electrolytes for LCM
  • Strategies for Industrial Use of LCM

In LCM the material removal is accomplished by the laser-induced chemical reaction between an electrolyte and the metal surface of the workpiece [Tani94] and depends mainly on the laser-induced temperature distribution over the workpiece surface [Mes17a]. A closer look at the SEM data of the resulting cavities in titanium (compare Fig.4.36 and 4.37) shows the differences in the removal quality depending on the electrolyte used. Figure 4.38 shows the influence of electrolyte concentration on the resulting removal depth in titanium using NaCl and NaNO3 solutions.

Table 4.5 Overview of the materials and electrolytes used for the experimental work
Table 4.5 Overview of the materials and electrolytes used for the experimental work

Hình ảnh

Fig. 1.5 Mastered aspects for a high quality and economic mass production of more than one million batches/micro parts
Fig. 2.2 Radiation strategy: a coaxial orientated laser beam, b lateral orientated laser beam [Br ü 16b]
Fig. 2.3 Comparison of energy fl uxes for the coaxial and lateral radiation strategy
Fig. 2.13 Comparison between humping during laser welding [Neu12] and irregularities during laser rim end melting
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