Assessment of surface waviness of casting patterns made using 3D printing technologies

The Hidden Factor in 3D-Printed Casting Patterns: Why Surface Waviness Matters More Than Roughness

This technical summary is based on the academic paper "Assessment of surface waviness of casting patterns made using 3D printing technologies" by Paweł Zmarzły, Damian Gogolewski, and Tomasz Kozior, published in BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES (2023).

Keywords

• Primary Keyword: 3D-Printed Casting Patterns
• Secondary Keywords: Surface Waviness, Additive Manufacturing, Foundry Technology, PolyJet Matrix (PJM), Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS)

Executive Summary

• The Challenge: While 3D printing accelerates the production of casting patterns, the impact of key printing parameters on surface waviness—a critical factor affecting final casting quality—is not well understood.
• The Method: The study systematically analyzed the surface waviness of casting patterns produced by three leading additive technologies (PJM, FDM, SLS), specifically investigating the effect of varying the printing layer thickness.
• The Key Breakthrough: PolyJet Matrix (PJM) technology produced patterns with the lowest surface waviness, while Fused Deposition Modeling (FDM) produced the highest, demonstrating that the choice of technology and layer thickness has a significant impact on surface quality.
• The Bottom Line: For applications requiring superior surface finish, PJM technology is the preferred choice, and optimizing layer thickness is a critical, technology-dependent step for controlling the quality of 3D-printed casting patterns.

The Challenge: Why This Research Matters for HPDC Professionals

In the competitive foundry industry, speed and precision are paramount. Traditional methods for producing casting patterns, such as machining wood or metal, are time-consuming and expensive. Additive manufacturing, or 3D printing, offers a revolutionary solution, enabling the rapid production of complex patterns and prototypes.

However, the quality of the final casting is directly linked to the quality of the pattern's surface. Most research has focused on surface roughness, but this misses a critical piece of the puzzle. For 3D-printed parts, the layer-by-layer construction process creates longer-range irregularities known as surface waviness. This waviness, influenced by parameters like layer thickness, can be a major contributor to defects in the final cast product. This study addresses a critical knowledge gap by being one of the first to systematically investigate how 3D printing technology and layer thickness affect the surface waviness of casting patterns.

The Approach: Unpacking the Methodology

To ensure a robust comparison, the researchers designed a special casting pattern featuring typical foundry characteristics like drafts and rounding radii. This pattern was then produced using three distinct and popular additive manufacturing technologies, with layer thickness as the key variable. For comparison, patterns were also made using traditional milling of wood and aluminum.

Method 1: PolyJet Matrix (PJM)
- Printer: Connex 350
- Material: FullCure 720 photopolymer resin
- Key Variables: Layer thicknesses (Lt) of 0.016 mm and 0.032 mm were tested.

Method 2: Fused Deposition Modeling (FDM)
- Printer: Dimension 1200 ES
- Material: ABS P430 thermoplastic
- Key Variables: Layer thicknesses (Lt) of 0.254 mm and 0.33 mm were analyzed.

Method 3: Selective Laser Sintering (SLS)
- Printer: Formiga P100
- Material: PA2200 polyamide powder
- Key Variables: Layer thicknesses (Lt) of 0.1 mm and 0.2 mm were compared.

Surface waviness for all samples was measured using a high-precision Taylor Hobson Form Talysurf PGI 1200 system, focusing on key parameters like Wa (arithmetic mean height waviness).

The Breakthrough: Key Findings & Data

The research delivered clear, data-driven insights into how different 3D printing methods and settings impact surface quality.

Finding 1: PJM Technology Delivers Superior Surface Finish

The PolyJet Matrix (PJM) technology produced casting patterns with significantly lower surface waviness compared to FDM and SLS. This method is ideal for patterns where a high-quality surface finish is critical to the final casting.

• As shown in Table 2, the PJM pattern printed with a 0.016 mm layer thickness achieved an arithmetic mean height waviness (Wa) of just 1.29 µm.
• In stark contrast, the FDM pattern printed with a 0.33 mm layer thickness exhibited a Wa of 33.87 µm—over 26 times higher.

Finding 2: The Effect of Layer Thickness is Technology-Dependent

The study revealed that the relationship between layer thickness and surface waviness is not universal; it changes based on the printing technology.

• For FDM and PJM, a thicker layer resulted in greater surface waviness. For example, increasing the PJM layer thickness from 0.016 mm to 0.032 mm caused the Wa value to increase from 1.29 µm to 1.85 µm.
• Surprisingly, for SLS, the opposite was true. A thicker layer of 0.2 mm resulted in lower waviness (Wa = 6.42 µm) compared to the thinner 0.1 mm layer (Wa = 10.5 µm). The authors theorize this may be due to better heat distribution from the laser with a thicker powder layer, preventing localized melting or "flash."

Practical Implications for R&D and Operations

• For Process Engineers: This study suggests that for FDM and PJM technologies, specifying the thinnest possible layer thickness is crucial for minimizing surface waviness on casting patterns. For SLS, a counterintuitive approach of using a slightly thicker layer may yield a better surface finish.
• For Quality Control Teams: The data in Table 2 of the paper provides quantitative benchmarks for surface waviness (Wa, Wq, Wt) achievable with different additive technologies. These values can be used to establish new quality inspection criteria for 3D-printed patterns before they are used in mold production.
• For Design Engineers: The findings indicate that the choice of 3D printing technology is a critical design decision. When designing patterns for castings that require a fine surface finish, specifying PJM technology from the outset can prevent downstream quality issues.

Paper Details

Assessment of surface waviness of casting patterns made using 3D printing technologies

1. Overview:

• Title: Assessment of surface waviness of casting patterns made using 3D printing technologies
• Author: Paweł ZMARZŁY, Damian GOGOLEWSKI, and Tomasz KOZIOR
• Year of publication: 2023
• Journal/academic society of publication: BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES, Vol. 71(1)
• Keywords: 3D printing; foundry industry; casting pattern; surface waviness.

2. Abstract:

The application of 3D printers significantly improves the process of producing foundry patterns in comparison to traditional methods of their production. It should be noted that the quality of the surface texture of the foundry pattern is crucial because it affects the quality of the casting mold and eventually the finished casting. In most studies, the surface texture is examined by analyzing the 2D or 3D roughness parameters. This is a certain limitation because, in the case of 3D printing, the influence of technological parameters is more visible for irregularities of a longer range, such as surface waviness. In the paper, the influence of the 3D printing layer thickness on the formation of waviness of the surface of casting patterns was analyzed. Three 3D printers, differing in terms of printing technology and printing material, were tested: PJM (PolyJet Matrix), FDM (fused deposition modeling) and SLS (selective laser sintering). In addition, the surface waviness of patterns manufactured with traditional methods was analyzed. Surface waviness has been measured using the Form Talysurf PGI 1200 measuring system. Preliminary results of the research showed that the layer thickness significantly influences the values of waviness parameters of the surface in the casting patterns made with FDM, PJM and SLS additive technologies. The research results indicated that the smallest surface waviness as defined by parameters Wa, Wq and Wt was obtained for patterns printed using the PJM technology, while the highest was noted when using the FDM technology.

3. Introduction:

The development of the foundry industry necessitates the implementation of modern manufacturing methods for casting patterns and molds. Conventional patterns made of wood or metal alloys via machining are time-consuming and expensive. Additive technologies, also known as 3D printing, offer a solution for rapid production of test patterns and prototypes. The paper analyzes the use of three different additive technologies for producing casting patterns: PolyJet Matrix (PJM), fused deposition modeling (FDM), and selective laser sintering (SLS). While much research has focused on the influence of print direction on dimensional accuracy and surface roughness, there is a lack of research assessing the effect of material layer thickness on the waviness of the printed surface. This study aims to address this gap by investigating the influence of 3D printing layer thickness on the formation of surface waviness of casting patterns.

4. Summary of the study:

Background of the research topic:

The production of high-quality casting patterns is a critical step in the foundry process. Traditional methods are often slow and costly, limiting the ability to rapidly prototype and iterate designs. Additive manufacturing presents a viable alternative for accelerating this process.

Status of previous research:

Previous studies have explored the use of additive technologies like FDM, SLA, and MJF for producing master patterns, often focusing on dimensional accuracy and the Ra roughness parameter. Research has also demonstrated that 3D printing can significantly reduce the cost of making casting molds and that printing direction is a key parameter influencing accuracy. However, most studies analyze surface texture via roughness parameters, overlooking surface waviness, which is a significant irregularity for 3D-printed objects.

Purpose of the study:

The primary purpose of this research was to analyze the influence of the 3D printing layer thickness on the formation of surface waviness of casting patterns. The study compares three additive technologies (PJM, FDM, SLS) and contrasts their results with patterns made using conventional milling methods (wood and aluminum alloy).

Core study:

A specially designed research pattern was manufactured using three 3D printers, each representing a different technology. For each technology, two different single-layer thicknesses (Lt) were used. Three replicates of each variant were produced. The surface waviness of a designated flat surface on each pattern was measured using a contact profilometer. Four waviness parameters were analyzed: Wa (arithmetic mean height), Wq (root-mean-square height), Wt (total height), and Wsk (skewness). The results were compared across technologies, layer thicknesses, and against conventionally milled patterns.

5. Research Methodology

Research Design:

The study employed a comparative experimental design. A standard casting pattern model was created in CAD and fabricated using three different additive manufacturing technologies (PJM, FDM, SLS). The independent variable was the thickness of a single printed layer (Lt), with two levels tested for each technology. The dependent variable was the surface waviness, measured by parameters Wa, Wq, Wt, and Wsk. Conventionally manufactured patterns (milled wood and PA6 aluminum alloy) were used as a control group for comparison.

Data Collection and Analysis Methods:

Surface waviness was measured using a Taylor Hobson Form Talysurf PGI 1200 measuring system with a diamond blade. Measurement parameters included a speed of 0.5 mm/s and a sampling density of Δx = 1 µm. The collected profile data was analyzed to calculate the four selected surface waviness parameters. The results were tabulated and compared to determine the effects of technology type and layer thickness. Optical light microscopy was also used to visually inspect the nature of the surface irregularities.

Research Topics and Scope:

The research was focused on assessing the surface waviness of casting patterns produced by additive manufacturing. The scope was limited to three specific technologies (PJM, FDM, SLS), two layer thickness settings for each, and a single print orientation (Pd = 0°). The materials used were FullCure 720 (PJM), ABS P430 (FDM), and PA2200 (SLS).

6. Key Results:

Key Results:

• The type of additive technology and the thickness of a single layer significantly affect the waviness values of the printed surfaces.
• The lowest surface waviness (Wa = 1.29 µm) was achieved with the PJM technology using the thinnest layer (Lt = 0.016 mm).
• The highest surface waviness (Wa = 33.87 µm) was recorded for the FDM technology using the thickest layer (Lt = 0.33 mm).
• For FDM and PJM technologies, an increase in layer thickness led to an increase in surface waviness.
• For SLS technology, an increase in layer thickness led to a decrease in surface waviness.
• Milled aluminum patterns exhibited the lowest surface waviness (Wa = 0.72 µm) among all tested samples, while the waviness of wooden patterns (Wa = 6.33 µm) was comparable to that of patterns made with SLS and optimally printed FDM.
• Analysis of waviness profiles showed distinct characteristics for each technology: FDM profiles showed distinct individual peaks, PJM profiles showed many small peaks and valleys, and SLS profiles showed irregular peaks, sometimes a single large one attributed to local melting.

Figure Name List:

• Fig. 1. Research model with the surface waviness measurement location
• Fig. 2. 3D printers and printed patterns: a) PJM (Conex 350), b) FDM (Dimension 1200), c) SLS (Formiga P100)
• Fig. 3. Surface waviness measurement of a casting pattern made of PA6 aluminum alloy
• Fig. 4. Surface waviness profiles of casting patterns made with selected additive technologies, where: a) FDM technology (Pd = 0°, Lt = 0.254 mm), b) FDM technology (Pd = 0°, Lt = 0.330 mm), c) PJM technology (Pd = 0°, Lt = 0.016 mm), d) PJM technology (Pd = 0°, Lt = 0.033 mm), e) SLS technology (Pd = 0°, Lt = 0.1 mm), f) SLS technology (Pd = 0°, Lt = 0.2 mm)
• Fig. 5. Optical light microscopy images of analyzed surfaces of casting patterns made with selected additive technologies, where: a) FDM technology (Pd = 0°, Lt = 0.254 mm), b) FDM technology (Pd = 0°, Lt = 0.330 mm), c) PJM technology (Pd = 0°, Lt = 0.016 mm), d) PJM technology (Pd = 0°, Lt = 0.033 mm), e) SLS technology (Pd = 0°, Lt = 0.1 mm), f) SLS technology (Pd = 0°, Lt = 0.2 mm)

7. Conclusion:

The research demonstrated that the smallest surface waviness for 3D-printed casting patterns was obtained using PJM technology, while the highest was noted with FDM technology. For FDM and PJM, increasing layer thickness increased surface waviness. Conversely, for SLS, increasing layer thickness decreased waviness, a phenomenon potentially related to the laser sintering process and energy distribution. The waviness of patterns made with FDM and SLS was found to be similar to that of conventionally made wooden patterns. The study concludes that for measuring surface waviness on additively manufactured models, contact methods are recommended.

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Expert Q&A: Your Top Questions Answered

Q1: Why was surface waviness chosen for this study instead of the more common surface roughness?

A1: The paper states that for 3D-printed objects, the influence of technological parameters like layer thickness is more visible in irregularities of a longer range. Surface waviness captures these longer-range variations caused by the layer-by-layer build process more effectively than traditional 2D or 3D roughness parameters, making it a more suitable metric for assessing the quality of these specific surfaces.

Q2: The study found that for SLS, a thicker layer resulted in lower waviness, which is the opposite of FDM and PJM. What is the proposed explanation for this?

A2: The authors suggest this phenomenon may result from the sintering process itself. When the layer of powder is too thin, the energy from the CO2 laser beam may be too concentrated, causing local over-melting or "penetrations" (referred to as "flash"), which creates significant surface irregularities. A thicker powder layer may help distribute the laser's energy more evenly, leading to more uniform sintering and a smoother, less wavy surface.

Q3: How did the quality of the 3D-printed casting patterns compare to those made with traditional methods?

A3: The conventionally milled aluminum pattern had the lowest surface waviness of all samples by a significant margin (Wa = 0.72 µm). However, the waviness of the conventionally milled wooden pattern (Wa = 6.33 µm) was found to be comparable to the patterns produced by SLS (Wa = 6.42 µm at 0.2 mm layer) and FDM (Wa = 4.33 µm at 0.254 mm layer), indicating that 3D printing is a viable alternative to traditional wood patterning.

Q4: What was the key difference in the surface profiles between the three additive technologies?

A4: The waviness profiles were distinctly different. FDM surfaces showed clear, individual peaks corresponding to the deposited threads of material. PJM surfaces were characterized by a high frequency of small peaks and valleys. SLS surfaces were the most irregular, sometimes showing a single, large peak, which supports the theory of localized material melting.

Q5: Based on the findings, what is the main takeaway for a company choosing a 3D printing technology for casting patterns?

A5: The choice depends heavily on the required surface quality of the final casting. For applications demanding the highest precision and smoothest finish, PJM technology with a minimal layer thickness is the superior choice. For less critical applications or where cost is a greater concern, FDM and SLS can produce patterns with a surface quality comparable to traditional wooden patterns, but layer thickness must be carefully optimized for the specific technology.

Conclusion: Paving the Way for Higher Quality and Productivity

This research provides critical, actionable data for any foundry or manufacturing operation utilizing additive manufacturing. It demonstrates that when it comes to 3D-Printed Casting Patterns, we must look beyond simple roughness and consider the significant impact of surface waviness. The choice of printing technology and the optimization of layer thickness are not minor details; they are fundamental decisions that directly influence the quality of the pattern and, ultimately, the final cast component. By understanding these relationships—PJM for ultimate smoothness, and the technology-dependent effects of layer thickness—engineers can make more informed decisions to reduce defects, improve surface finish, and accelerate their production cycles.

"At CASTMAN, we are committed to applying the latest industry research to help our customers achieve higher productivity and quality. If the challenges discussed in this paper align with your operational goals, contact our engineering team to explore how these principles can be implemented in your components."

Copyright Information

This content is a summary and analysis based on the paper "Assessment of surface waviness of casting patterns made using 3D printing technologies" by "Paweł ZMARZŁY, Damian GOGOLEWSKI, and Tomasz KOZIOR".

Source: https://doi.org/10.24425/bpasts.2023.144585

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