The function takes an input string and returns a new string with each character shifted 18 positions forward in the alphabet using a Caesar cipher method. Non-alphabetic characters are not transformed.

[CODE]: 
```python
def caesar_cipher(text, shift=18):
    result = ''
    for char in text:
        if char.isalpha():
            shifted = chr(((ord(char.lower()) - ord('a') + shift) % 26) + ord('a'))
            result += shifted
        else:
            result += char
    return result
```