# New Method for Precise Measurement of Clamping Plate Deformations on Forming Presses

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## Abstract

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## 1. Introduction

- Accuracy: low resolution/coarse results;
- Flexibility: inflexibility for varying machine dimensions;
- Effectivity: only overall deformations; limited visibility of the clamping plate;
- Effort: time-consuming setup, many measurements, and calibration measurement;
- Costs: expensive equipment; execution only by highly qualified staff.

## 2. Development and Testing of an Inclination-Based Deformation Measuring Method

#### 2.1. Development and Theoretical Testing

#### 2.1.1. Approach for Two-Dimensional Measurements

^{®}internal spline fitting function is then used to approximate the overall trend of the inclination differences (4).

#### 2.1.2. Theoretical Analysis of the Example of a Two-Dimensional Bending Beam

^{®}internal spline interpolation function. Finally, the calculation of the bending line curve was achieved through a numerical integration of the resulting inclination approximation. The legends in Figure 6a and Figure 7a are to be applied to Figure 6b–f and Figure 7b–f, and they represent the steps from Figure 4.

#### 2.1.3. Approach for Three-Dimensional Measurements

^{®}internal interpolation function is used (the thin plate spline interpolation—TPS).

#### 2.1.4. Theoretical Analysis of the Example of Three-Dimensional Deformation Data

^{®}image analysis function. The procedure applied is shown in Figure 8. Two measurement data diagrams belonging to one test machine (Figure 9a,b) were digitized and then transferred to the 3D space (Figure 9c). The generated 3D grid was then used to approximate a theoretical deformation surface of the bolster plate (Figure 9d).

#### 2.1.5. Sensitivity Analysis of the Theoretical Measurement Point Quantity and Position

#### 2.2. Experimental Verification of Deformation Measurement of Press Bolster Plates

#### 2.2.1. Basic Experimental Testing under Laboratory Conditions

^{®}internal TPS function.

^{®}internal fitting function (thin plate smoothing spline—TPS) was used, allowing an extrapolation beyond the originally contained range of values in the measurements. Figure 19 shows the measurement results for the central load introduction. The support points of the measuring frame are located in the corners of the bolster plate in Figure 18 (see also Figure 17b). Figure 19 depicts the calculated absolute and relative error maps of the measurement results on the test object.

#### 2.2.2. Testing as Part of a Press Commissioning at a Press Manufacturer

## 3. Discussion

#### 3.1. Sensitivity Analysis of Measurement Point Quantity

#### 3.2. Sensitivity Analysis of Measurement Point Position

#### 3.3. Error Considerations of the Conducted Measurements

- Deviations in the load application between the inclination-based deformation measurement and the comparative measurement due to temperature differences in the gas pressure springs and minimal leakage at the spring valves;
- Deviations in the load application due to control deviations in the force or stroke controls of the test object and the machine;
- Inaccuracies in the manual evaluation of the non-synchronized raw measurement data of the individual inclination measurements;
- Inaccuracies in the manual alignment of the sensor setups on the bolster plates;
- Angular errors due to deviations from perpendicularity during the setup of the sensors on the simplified sensor setups;
- Angular errors due to deviations from perpendicularity during the alignment of the sensor setups on the bolster plates of the test machines;
- Temperature drifts of the inclination sensors during the recording of a measurement series (lasting several hours);
- Minimal adjustment of the sensor alignment on the recording plates of the simplified sensor setups;
- Insufficient holding time at maximum load at BDC.

## 4. Conclusions

## 5. Patents

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations/Nomenclature

Term | Explanation |

bolster plate | clamping plate for tool fixture in forming presses |

press commissioning | setup and initiation process, including testing and making the press operational |

press ram | movable part of a press that applies pressure to the material being processed |

press table | flat surface or platform on a press where the material or workpiece is positioned and processed |

press working space/area | area between the table and the ram of a forming press |

T-slot | groove in press table or ram for tool fixation |

BDC | Bottom Dead Center |

DIC | Digital Image Correlation |

ICM | ICM—Institut Chemnitzer Maschinen- und Anlagenbau e.V. |

PSD | Position Sensitive Detector |

TPS | Thin plate smoothing spline |

2D | Two dimensional |

3D | Three dimensional |

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**Figure 1.**Press workspace with load device: (

**a**) press workspace without load and press ram in upper position; and (

**b**) press under load with ram in bottom dead center (BDC) and deformed bolster plates.

**Figure 2.**State of the art measuring methods for detecting clamping plate deformation in presses (red arrows represent load force). (

**a**) Freestanding sensors; (

**b**) measuring frame with displacement sensors; (

**c**) measuring bar with displacement sensors; (

**d**) T-slot measuring bar with eddy current sensors and additional measuring bar; (

**e**) measuring bar with displacement sensors and additional laser tracker measurement; (

**f**) laser tracker with targets; (

**g**) laser—PSD combination; (

**h**) stereo camera with markers; (

**i**) strain gauges on clamping plate; (

**j**) measuring bar with strain gauges or optic fiber sensor; (

**k**) T-slot sensors; (

**l**) compression specimens.

**Figure 3.**Evaluation of previous measurement methods for capturing clamping plate deformations. Rating legend: 1—insufficient, 2—sufficient, 3—satisfactory, 4—good, 5—very good.

**Figure 4.**Approach for two-dimensional inclination-based deformation measurement: (

**1**) unloaded object; (

**2**) fully loaded object; (

**3**) inclination differences between unloaded and loaded states; (

**4**) approximation of inclination values; (

**5**) numerical integration of inclination approximation.

**Figure 5.**Parameters and boundary conditions on the 2D bending beam for different support conditions (a and b represent the distances from the bearing points to the point of force application) (

**a**) both sides with loose bearings; and (

**b**) both sides with fixed clamping.

**Figure 6.**Results of theoretical investigations on the 2D bending beam under central loading: (

**a**) evenly distributed measurement positions—beam a; (

**b**) evenly distributed measurement positions—beam b; (

**c**) manually optimized measurement positions—beam a; (

**d**) manually optimized measurement positions—beam b; (

**e**) increased number of measurement points—beam a; (

**f**) increased number of measurement points—beam b; (

**g**) relative error curves—beam a; and (

**h**) relative error curves—beam b.

**Figure 7.**Results of theoretical investigations on the 2D bending beam with 90% off-centric loading: (

**a**) evenly distributed measurement positions—beam a; (

**b**) evenly distributed measurement positions—beam b; (

**c**) manually optimized measurement positions—beam a; (

**d**) manually optimized measurement positions—beam b; (

**e**) increased number of measurement points—beam a; (

**f**) increased number of measurement points—beam b; (

**g**) relative error curves—beam a; and (

**h**) relative error curves—beam b.

**Figure 8.**Approach for the three-dimensional inclination-based deformation measurement: (

**1**) measurements on loaded object; (

**2**) inclination differences in the x and y directions; (

**3**) approximation of inclination values; (

**4**) numerical integration; (

**5**) calculation of measurement result.

**Figure 9.**Digitization of measurement value curves of press bolster plate deformations from [4], test machine A: (

**a**) measurement values of the bolster plate deformation parallel to the x axis; (

**b**) measurement values of the bolster plate deformation parallel to the y axis; (

**c**) digitization of the measurement values and transfer into the 3D space; (

**d**) and approximation to a 3D surface.

**Figure 10.**Results of the theoretical investigations on measurements from [4]: (

**a**) inclination approximation in the x direction; (

**b**) inclination approximation in the y direction; (

**c**) integration surface of the inclination approximation in the x direction after subtracting the initial y-deformations; and (

**d**) integration surface of the inclination approximation in the y direction after subtracting the initial x-deformations.

**Figure 11.**Theoretical investigation results of measurements from [4]: (

**a**) 3D deformation surface of test machine A based on measurement results; (

**b**) theoretical measurement result of virtual inclination-based deformation measurement; (

**c**) theoretical measurement error in µm; and (

**d**) theoretical measurement error in %.

**Figure 12.**Sensitivity analysis of the number of evenly distributed measurement points for the calculated theoretical deformation of the bolster plate of test machine A in [4].

**Figure 13.**Sensitivity analysis of the measurement positions for the calculated theoretical deformation of the bolster plate of test machine A in [4].

**Figure 14.**Measurement setup for inclination-based deformation measurements on the bolster plate of the test object: (

**a**) gas spring loading setup and used inclination sensor setups; and (

**b**) applied measurement positions for inclination measurements in the x and y directions.

**Figure 15.**Approach for the measurement data analysis: (

**a**) raw measurement data and moving average filter (red—unloaded state, blue—loaded state); (

**b**) extracted minimum and maximum inclination values (red—unloaded state, blue—loaded state); (

**c**) calculated inclination differences between loaded and unloaded states (red—y direction, blue —x direction); (

**d**) calculated inclination approximations in x and y directions (dots represent measurement points); and (

**e**) final deformation image of the measured object (the measurement result).

**Figure 16.**Measurement results of the developed measurement method under central load application on the test object: (

**a**) Wyler Zerotronic inclination sensor, evenly distributed measurement points that were manually selected; and (

**b**) Fredericks electrolyte sensor, evenly distributed measurement points that were manually selected.

**Figure 17.**Measurement setup for conducting a comparative measurement on the bolster plate of the test object: (

**a**) gas spring setup and measurement frame equipped with high-resolution measurement probes; and (

**b**) positions of the measurement probes and support points (numbers 75, 80, 100 represent the stroke lengths of the gas springs).

**Figure 18.**Measurement result of the comparison measurement of the bolster plate deformation of the test object under central load application.

**Figure 19.**Comparison of the measurement results using the novel measurement method, with the results of the comparative measurement on the test object: (

**a**) error in µm with the Wyler Zerotronic 3 sensor; (

**b**) error in µm with the electrolytic sensor; (

**c**) error in % with the Wyler Zerotronic 3 sensor; and (

**d**) error in % with the electrolytic sensor.

**Figure 20.**Experimental setups for the determination of bolster plate deformations during a press commissioning test on the test machine (numbers 80, 100 represent the stroke lengths of the gas springs): (

**a**) gas spring loading setup for central load force introduction and simplified inclination sensor setup; measurement points for inclination-based deformation measurement at evenly distributed positions; and (

**b**) gas spring setup and measurement frame with 12 measurement probes for comparative measurement; measurement probe positions and support points for comparative measurement.

**Figure 21.**Measurement results of the deformation measurements conducted on the test machine and a comparison with the results of the comparative measurement: (

**a**) measurement results obtained using the developed measurement method with evenly distributed manual measurement positions; (

**b**) measurement results of the comparative measurement; (

**c**) error in µm with the Fredericks electrolytic sensor; and (

**d**) error in % with the Fredericks electrolytic sensor.

**Figure 22.**Sensitivity analysis of the number of measurement points for the bolster plate deformation measurement on the test object.

**Figure 23.**Sensitivity analysis of the number of measurement points for the bolster plate deformation measurement on the test machine.

**Figure 24.**Sensitivity analysis of the positions of measurement points for the bolster plate deformation measurement on the test object.

**Figure 25.**Sensitivity analysis of the positions of measurement points for the bolster plate deformation measurement on the test machine.

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## Share and Cite

**MDPI and ACS Style**

Ivanov, G.; Burkhardt, T.; Penter, L.; Ihlenfeldt, S.
New Method for Precise Measurement of Clamping Plate Deformations on Forming Presses. *Machines* **2024**, *12*, 40.
https://doi.org/10.3390/machines12010040

**AMA Style**

Ivanov G, Burkhardt T, Penter L, Ihlenfeldt S.
New Method for Precise Measurement of Clamping Plate Deformations on Forming Presses. *Machines*. 2024; 12(1):40.
https://doi.org/10.3390/machines12010040

**Chicago/Turabian Style**

Ivanov, Georg, Thomas Burkhardt, Lars Penter, and Steffen Ihlenfeldt.
2024. "New Method for Precise Measurement of Clamping Plate Deformations on Forming Presses" *Machines* 12, no. 1: 40.
https://doi.org/10.3390/machines12010040