Tag: Milling Programming

Listen up, fellas! Master Wang here. Today, we’re skipping the theory and diving straight into solid practical application. This part we’ve got here might look simple, but without a proper plan, you’re guaranteed to run into all sorts of headaches during machining. So today, let’s talk about how to tackle its connecting rib modeling and programming using NX, ensuring your work is both fast and stable.

Part Geometry Analysis and Machining Challenges

Quickly Identifying Machining Difficulties

When you get a part, the first step isn’t to rush into the software. Instead, you need to look closely and analyze it thoroughly. As you’ll see, this part may appear simple, but we first need to understand its ‘characteristics’.

• Connecting Rib Strategy: For parts like this, creating connecting ribs on the left and right sides is usually straightforward. However, pay attention: there’s an angled face at the front, which isn’t ideal for direct connection. So, we need to adapt flexibly: focus on connecting the left and right sides, while avoiding the angled face.
• Surface Finish Issues (Flashing Surface): From a top view, some areas of this part show tool marks, which are what we often call ‘machined surfaces’ or ‘surfaces being cut’. But from a bottom view, these marks disappear. This tells us that during programming, we must pay close attention to the cutting direction and tool entry points in these areas to avoid leaving unsightly tool marks on critical surfaces.
• Angled and Flat Surface Combination: The part’s sides have distinct angled faces, indicating that subsequent machining will definitely involve tilted machining or 5-axis simultaneous machining (if high precision is required). However, most other areas are flat, which simplifies roughing.

Key Dimensions and Radius (R) Corner Confirmation

After analyzing the shape, you need to examine the dimensions. Don’t just glance at the general outline; the detailed R corners and clearances will dictate which tool you select and how you program the tool path.

• Uniform R Corners: We just checked, and all internal R corners are R3. This is excellent, as it means for the finishing pass, a single R3 ball end mill or bull nose end mill can handle most of the details, saving the hassle of frequent tool changes.
• Connecting Rib Reserved Width: Ultimately, we need to cut off the connecting ribs, which requires reserving sufficient width for tool clearance. For example, measurements show the connecting locations are approximately 12.5mm (approx. 0.49 inch) apart. This gives us ample space to select an appropriate tool for cutting, such as a Ø10mm (approx. 0.39 inch) end mill. Even a Ø8mm (approx. 0.31 inch) tool could work, but you’d need to consider its rigidity and the cutting forces.

Core Techniques for NX Auxiliary Body Modeling

An auxiliary body isn’t just a random sketch; it’s crucial for securely clamping your part on the machine while enabling efficient machining. Listen up, this is the real expertise you won’t find in textbooks.

Function and Preliminary Preparation of Auxiliary Bodies

Why create an auxiliary body? It’s simple: it provides you with a secure clamping point, preventing the part from vibrating or deforming during machining. Concurrently, it defines your machining area, preventing the tool from cutting unintended regions.

1. Copy the Part: First, copy the original part to different layers. This is good practice to avoid directly modifying the original model.
2. Create Stock / Bounding Body: Typically, we start by creating a simple bounding body, such as a rectangular block, as the starting point for subsequent auxiliary body construction. Then, delete the original part, retaining only the bounding body for further operations.
3. Set WCS (Work Coordinate System): Ensure the coordinate system is set up correctly; this is the foundation for all programming.

Generating Auxiliary Curves from Tool Path Trajectories

Master Wang will teach you a trick: directly generate the tool path using the machining module, then extract the tool path boundary to create auxiliary lines. This method offers high efficiency and accurate precision!

1. Select Machining Operation: We’ll use “Cavity Milling” or a similar roughing strategy, selecting the target face. Note: this isn’t for 5-axis “Contour Profile,” which is used for finishing passes.
2. Tool Selection: Here, choose a larger tool, such as a Ø25mm (approx. 0.98 inch) end mill. The goal is to quickly generate a rough trajectory around the machining area. Keep only the final cutting layer to retain the bottom trajectory.
3. Extract Boundary Curve: After generating the tool path, use the “Analysis Tool” and its “Extract Boundary” function to extract the outermost boundary of this tool path. This curve will be the initial shape of your connecting rib.
4. Curve Extension: The extracted curve should be extended outwards appropriately (e.g., 20mm (approx. 0.79 inch)) so it extends beyond the part’s main body. This ensures that when performing the cut-off operation later, the tool can fully exit the material, preventing remnants.

Auxiliary Body Thickening and Trimming

Once you have the boundary, how do you turn it into a solid connecting rib? This requires using “Thicken” and “Boolean operations.”

1. Create Sheet Body and Thicken:
   

   • Select the extracted boundary curve and use the “Extend Face” or “Extrude” command to extrude it into a sheet body, which will serve as the base face for the connecting rib. Pay attention to the extrusion direction and height to ensure it fully encompasses the part.
   • Then, perform a “Thicken” operation on this sheet body. For instance, if you’ve left a 1mm (approx. 0.04 inch) allowance, the sheet body’s thickness can be set to 19mm (approx. 0.75 inch), making the total height 20mm (approx. 0.79 inch). Check all faces to ensure a 1mm (approx. 0.04 inch) machining allowance is maintained everywhere.

2. Boolean Operation Trimming:
   

   • Perform a “Subtract” Boolean operation between the thickened auxiliary body and the original part. Subtract the original part from the thickened auxiliary body. What remains will be the connecting ribs, conforming to the part’s outer shape and maintaining a clearance from the main part body.
   • Carefully inspect the trimmed auxiliary body to ensure there’s a clear clearance between it and the main part body, and that the connecting rib shape is robust and reliable. If certain areas don’t require extrusion or thickening, retain the original face and handle them flexibly.

Process Planning and Tool Selection

Roughing and Finishing Allowance Settings

Setting allowances is an art, directly impacting tool life, machining efficiency, and final precision.

• Uniform Allowance: When creating the auxiliary body, we ensured a 1mm (approx. 0.04 inch) allowance was left all around. This allowance is suitable for subsequent roughing and semi-finishing operations. It guarantees sufficient Depth of Cut (DOC) during roughing without being excessive, which could overburden the finishing pass.
• Staged Machining: Roughing should be fast, aggressive, and accurate, removing the bulk of the material. Semi-finishing aims for a smooth transition, preparing for the finishing pass. The finishing pass is precision work, focused on achieving surface finish and accuracy, requiring a small allowance and sharp tools.

Connecting Rib Width and Tool Diameter Matching

The width of the connecting ribs directly dictates which tool you use for the cut-off operation. Selecting the wrong tool can lead to minor issues like tool breakage, or major problems like a scrapped workpiece.

• Width Calculation: Our connecting ribs have a width of at least 12.5mm (approx. 0.49 inch) at their narrowest point. So, choosing a Ø10mm (approx. 0.39 inch) end mill for the cut-off is perfectly fine; the tool’s rigidity is good, and cutting will be stable. If you want to leave a small finishing allowance, you could even opt for a Ø8mm (approx. 0.31 inch) tool, but you must control the speed and feed rates carefully to avoid overloading the tool.
• Safety Clearance: For cut-off tool paths, always ensure the tool can fully exit the material. Don’t restrict the cut inside the workpiece – that’s called “confined cutting,” which can easily lead to chatter, chipping, or even tool breakage. Therefore, when modeling, we intentionally extend the auxiliary body’s edges slightly beyond the cut-off path to allow the tool to enter and exit freely.

Tool Path Optimization Principles

A well-optimized tool path doubles efficiency and extends tool life.

• Reduce Air Cuts: NX offers various tool path optimization features, such as “Rest Milling” and “Steep/Non-Steep Area Differentiation.” Strive to keep the tool working within the cutting area, minimizing tool retracts and idle movements.
• Prioritize Climb Milling: In most cases, opt for climb milling; it provides more stable cutting and a better surface finish. Conventional milling can easily lead to tool slippage and chatter.
• Appropriate Feed Rates: This relies on experience, don’t just go by software parameters. During actual machining, observe the cutting sparks, listen to the cutting sound, and feel the chip temperature, then gradually adjust to achieve optimal performance.

Summary: Pitfall Avoidance Guide

1. Analysis First: Always remember, analyze the part before you rush into anything. Understand its geometric features, R corner sizes, and which faces are critical, only then can you devise the correct machining strategy.
2. Auxiliary Bodies Aren’t Random Sketches: An auxiliary body is the bridge connecting your design intent to machining reality. It must be sufficiently robust to withstand cutting forces; its shape should be rational to allow easy tool entry and exit; and its dimensions must be precise, matching the machining allowance.
3. Tool Selection and Path Planning: Select the appropriate tool based on material properties, part R corners, and connecting rib width. Tool path planning must consider efficiency, tool life, and surface finish. Make good use of NX’s optimization features to reduce air cuts.
4. Allowance is Key: Precisely controlling the allowances for roughing, semi-finishing, and finishing passes is fundamental to ensuring final precision and surface finish. Too little can result in an insufficient surface finish, while too much can cause chatter.
5. Practical Experience is Paramount: No matter how good the software simulation looks, it doesn’t compare to real cutting with sparks flying on the shop floor. Observe more, think more, summarize more. Only by combining textbook knowledge with practical application can you truly become an expert. Don’t just watch software simulations; look at the cutting sparks!